CN1691087A - System and method for decoding digitally encoded images - Google Patents

Abstract

The invention provides a method of decoding coding image produced by main image and at least one auxiliary image utilizing at least one coding parameter. The said coding image is formed as the following method: when printing the coding image, the viewers can not distinguish the auxiliary image without an optics decoding device which has the corresponding characteristic with at least one coding parameter. The said method includes: obtaining the digital edition of the said coded image; confirming at least one code parameter mentioned above; and utilizing at least one code parameter in the said code population of parameters to make up the decoding image of the said digital coding image.

Description

System and method for decoding digitally encoded images

Cross References to Related Applications

This application claims priority to US Provisional Application No. 60/565,300, filed April 26, 2004, the entire disclosure of which is incorporated herein by reference. This application is also related to U.S. Application No. 10/847,962 (the '962 application), filed May 18, 2004 (the '962 application) and U.S. application No. 10/897,943 (the '943 application), filed May 18, 2004, which are hereby incorporated in their entirety published together as a reference.

technical field

The present invention relates generally to the field of counterfeit protection and more particularly to the field of electronic and printed document protection through the use of coded images.

Background technique

There is an emerging trend in the ever-changing world of electronic commerce to use the World Wide Web and electronic mail to provide consumers and other end users with up-to-date business documents. Automating document generation and electronic distribution, such as using electronic mail or World Wide Web services, has many advantages. This significantly reduces costs associated with pre-printed forms, document filing, mailing, handling, and the like. It gives industry users instant access to important data and keeps documents always available to customers throughout the day. However, electronic documents have certain drawbacks, including the potential to tamper with or create a deceptive document that resembles the original in most or all respects.

Many software tools have been proposed to protect the integrity and confidentiality of electronic documents. Tools such as plug-ins can provide extensive control over adding or modifying records and forming fields in electronic documents, encrypting documents, and adding digital signatures to documents.

A significant disadvantage of protection measures typically used to protect documents placed in electronic form is that these measures are often useless once the document has been transferred to a print medium. Furthermore, typical hard copy protection measures are not available to recipients of electronic documents. For example, secure ink or paper is available to the creator of the document but not to the recipient of the electronically transmitted document. Clearly, there are problems with maintaining the security of hard copies of electronic transmission copies when the creator of the document has no control over the printing process. Additionally, many desktop image editing software tools can be used to create fake printouts of very complex electronic documents. Printed documents are also widely used in many aspects of everyday life, including business and government facilities.

Widely used protection methods against digital forgery and alteration of identifying data include barcodes and digital watermarks. Typically, these are added to the document by the originating party as image files. However, barcode generation software is widely available and can be used by counterfeiters to create deceptive documents.

Digital watermarking has been proposed as a solution, but testing has shown that it may lack the consistency and reliability required for widespread use. Furthermore, implementing such technologies is often expensive, with the cost of equipment for the necessary hardware and software sometimes offsetting the cost savings achieved through electronic document distribution. Typically, the amount of information that can be protected can be limited to just a few numbers or letters. These problems impose serious constraints on the reliability and usability of electronic documents in commerce and services.

The forgery and alteration of printed documents and the black market sale of counterfeit goods are significant problems facing the increasing regulation of today's world. Millions of dollars are lost each year due to the deceptive use of non-authentic documents and branded merchandise. The increasing sophistication of optical scanners, copiers, and other equipment used to reproduce items continues to increase the ability of counterfeiters to produce fraudulent documents and other forgeries of sufficient quality to often go undetected.

Protection of documents has been achieved by applying coded images. Typically, such images cannot be resolved or interpreted without a purpose-built optical decoder. In fact, use it on any form of printed document, including legal documents, ID cards and paperwork, labels, packaging, currency, stamps, and more. The value of using non-reproducible encoded images on documents such as driver's licenses and vehicle titles is obvious. In addition, its use on packaging as a method of identifying counterfeit goods is also of high value.

The use of encoded images greatly enhances the ability to detect forged and altered documents. However, there are situations where it is impractical to use an optical decoder to detect encoded images. There are other situations where it is desirable to use encoded images to protect documents even before they are printed. In both of these types of situations (and others), it is highly desirable to have a digital or software based decoder for decoding digitally encoded images. It may also be necessary to combine the use of coded images with the use of other protection measures.

Contents of the invention

The present invention proposes a data processing system and method for decoding digitally encoded images. One aspect of the invention proposes a method for decoding an encoded image resulting from a main image and at least one auxiliary image using at least one encoding parameter. Said encoded image is formed in such a way that when the encoded image is printed, the auxiliary image cannot be discerned by a viewer without an optical decoding device having characteristics corresponding to said at least one encoding parameter. The method includes: obtaining a digital version of the encoded image; determining the at least one encoding parameter; and constructing a decoded image from the digitally encoded image using at least one encoding parameter in the set of encoding parameters.

Another aspect of the invention proposes a method for enhancing the protection of a digital document in which a first coded image has been embedded, said first coded image having been constructed using a set of verification contents and a set of first coding parameters. The method includes: digitally decoding the first encoded image by using the first encoding parameter set to generate a decoded image; extracting the verification content set from the decoded image. Then, construct a second encoded image by using the verification content set and the second encoding parameter set.

Description of drawings

The present invention will be more fully understood by reading the following description together with the accompanying drawings, in which like reference characters are used to refer to like components, wherein:

Figure 1 is a diagram of decoding a print-encoded image using an optical decoder;

Figure 2 is a diagram of a typical rasterized encoded image formed from a main image and an auxiliary image using a raster conversion method;

Figure 3 is a diagram of decoding the encoded image shown in Figure 2 using an optical decoder;

Figure 4 is a graph of a blank control image with periodically varying tone densities;

Figure 5 is a diagram of an auxiliary image embedded in the contrast image shown in Figure 4;

Figure 6 is an encoded image formed from the main image and the contrast image shown in Figure 5;

7 is a flowchart of a method for decoding a digital image according to an embodiment of the present invention;

8 is a flowchart of a method for decoding a digital image according to an embodiment of the present invention;

9 is a flowchart of a method for decoding a digital image according to an embodiment of the present invention;

Fig. 10 is a schematic diagram of sampling a coded image;

FIG. 11 is a schematic diagram of a composite image formed from the coded image samples shown in FIG. 10;

12 is a flow chart of a method for protecting and verifying a digital document according to an embodiment of the present invention;

Figure 13 is a schematic diagram of a system for protecting and authenticating digital documents according to an embodiment of the present invention;

Figure 14 is a schematic diagram of a system for protecting and authenticating digital documents according to an embodiment of the present invention;

FIG. 15 is a flowchart of a method of protecting and authenticating a digital document, according to an embodiment of the present invention.

Detailed ways

The present invention proposes a method for decoding digitally encoded images without the use of physical optical decoding devices. These methods can be used to decode digitally encoded images that have never been printed, as well as printed encoded images that have been scanned or converted to digital form by other means. The ability to decode digital images allows users to protect against tampering with documents in both digital and printed form, thus bridging the digital to paper boundary. Additional security is provided by allowing authentication and modification of encoded images at different stages of electronic document generation, transmission and printing.

Embodiments of the invention relate to methods of securing documents and other items using optically encoded images. Typically, these images are embedded in the background or source image and printed on the entry which may be altered, altered or counterfeited. As used herein, the term "encoded image" refers to an image that has been manipulated or hidden within a background field or another image in such a way that it cannot be discerned by the human eye without the use of a decoding device when applied or printed. Encode the image. Some coded images are hidden, making their presence difficult to discern from the background or main image. Other encoded images are easily visible but not readable because the image content has been systematically scrambled or otherwise processed.

Coded images of particular importance to the invention are those configured for optical decoding using a lenticular lens. This image exploits the ability of a lenticular lens to mask image content based on the lens' microlens frequency. Typically, these images are encoded by one of several methods that involve creating a regularized periodic pattern with a frequency corresponding to the lenticular lens to be used as a decoder, and then causing the pattern to deform so that the image is difficult to use. Identify with the naked eye. Such encoded images may be formed analogously, as disclosed in U.S. Patent No. 3,937,565, or digitally, as disclosed in U.S. Patent 5,708,717 (the '717 patent), using specialized photographic equipment As stated, its entire disclosure is hereby incorporated by reference.

A digitally encoded image may be embedded in a background or other graphic image, making the presence of the encoded image difficult to discern. Referring to FIG. 1 , an encoded image 10 may be formed using a main or source image 20 and an auxiliary image 40 embedded in the main image 20 in such a manner that the auxiliary image 40 may only be viewed with a decoding device 40 of a predetermined frequency. The main image may be a blank gray or colored background image, like the coded image 10 shown in Figure 1, or may include visual image content such as a drawing or photograph or any other form of indicia. Additionally, the secondary image may be any form of image or indicia, and may include indicia that are in some way related to the primary image. In the example encoded image 10, the auxiliary image 40 is a repeating pattern based on the words "Department of Transportation". The auxiliary image can be encoded separately and then incorporated or embedded into the main image, or the embedding process can be implemented in such a way that the auxiliary image is encoded when it is embedded. As shown in FIG. 1 , the auxiliary image can be viewed by placing the decoding device 40 over the encoded image 10 in a suitable orientation. In the example of FIG. 1 , the decoding device has a horizontal axis 32 and a vertical axis 34 , while the encoded image 10 has a horizontal axis 22 and a vertical axis 24 . When the horizontal axis 32 of the decoding device 40 is oriented at a decoding angle α relative to the horizontal axis 22 of the coded image 10 , the auxiliary image 40 is revealed. The decoding angle α is an encoding parameter established before encoding and embedding of the auxiliary image.

The methods by which the auxiliary image is embedded or merged into the main image can be divided into two general methods. In a first approach, a regularized periodic behavior is imposed on the main image using a predetermined frequency. This is primarily achieved by rasterizing the main image at a predetermined frequency. The auxiliary image is then mapped to the main image so that regularization properties of the main image can be changed at positions corresponding to positions in the auxiliary image comprising image content. The change is small, but makes it difficult to discern by the human eye. However, when a lenticular lens having a frequency corresponding to a predetermined frequency is placed over the main image, it will mask the main image content in such a way that this change is extracted to form a hidden auxiliary image.

In the second method, firstly, a regularized periodic characteristic is imposed on the auxiliary image instead of the main image, a change of this characteristic occurs whenever there is content in the auxiliary image. Then, the auxiliary image is mapped to the main image, and the content of the main image is changed pixel by pixel according to the content of the encoded auxiliary image.

An example of the above method will now be discussed in more detail. A simple example of the first method is shown in Figures 2-3. FIG. 2 shows an enlarged view of the optically encoded image 110 . The coded image 110 is composed of a main image of a human face and an auxiliary image of the letters "SI". Rasterize the main image with a specific mask frequency and raster angle α. The auxiliary image is embedded into the main image by introducing a position change (movement) of the raster elements at positions corresponding to the content of the auxiliary image. These variations can be made small enough that it is difficult or impossible for the human eye to interpret them as a cohesive image embedded in the main image. Its presence can be further disguised by making the transition from the unaltered raster part of the image to the altered part as gradual and smooth as possible. The result, as shown in FIG. 2, is an encoded image 110 in which the main image is easy to view, but the auxiliary image is not easy to distinguish. As shown in FIG. 3 , when a lenticular decoding lens 120 with a line frequency corresponding to the masking frequency is placed over the encoded image 110 in a suitable orientation (i.e., grating angle α), the auxiliary image (letter "SI ").

The presence of embedded images can be further masked by compensating for the tonal density of smaller areas or windows of the main image. This is achieved by modifying individual pixels in the shifted image so that the average tone density of each window remains the same as the corresponding window of the unshifted image.

Those of ordinary skill in the art will appreciate that the methods described above can be used with any form of point, symbol or line rasterization. Furthermore, this method and others can be used to embed multiple auxiliary images with different encoding parameters as disclosed in the pending '962 and '943 applications.

A method somewhat similar to that described above is disclosed in the '717 patent. In this method, the auxiliary image is first encoded using the scrambling method disclosed in the '717 patent, and then the raster lines of the main image are reshaped to follow the pattern of the encoded auxiliary image. The resulting embedded image can be viewed using a lenticular decoding device with the same frequency used to rasterize the main image and encode the auxiliary image.

If you want the output image to be a continuous-tone image (as opposed to the rasterized image produced by the first method), you can use the second general method of embedding an auxiliary image into the main image. In this method, an auxiliary image is embedded into a "blank" control image that contains nothing but regularized periodic tonal changes. Then, a control image (control image) with an embedded auxiliary image is mapped to the main image.

Now, based on Figures 4-6, a simple example of this method will be discussed. FIG. 4 shows a blank control image 210 in which the tonal values of the pixels of the image are changed according to a periodic function such as a square wave, a sine wave, a triangle wave, and the like. The frequency of this function matches that of the lenticular decoding lens. The periodically varying angular directions form the angles used to decode the encoded image. As shown in FIG. 5, the auxiliary image 220 is embedded into the control image 210 by shifting the phase of the periodic function at any location corresponding to the location of the content in the auxiliary image. In this way, the deviation from the regularized tonal variation in the modified comparison image 210 corresponds to the content of the auxiliary image.

Then, the modified control image 210 is mapped pixel by pixel to the main image 230 . Pixels of the master image 230 are lightened or darkened to match the pattern of hue changes of corresponding pixels in the control image 210 . The final coded image is shown in FIG. 6 . The actual amount to brighten or darken the main image pixel can be determined using a transformation function, usually defined as a lookup table. These functions can be different, depending on the imaging application. For example, transfer functions can be designed to be specific to a particular printing process (eg, inkjet, dye sublimation, laser printing).

Those of ordinary skill in the art will appreciate that the methods described above can be used to embed multiple auxiliary images with different encoding parameters as described in the co-pending '962 application and the '943 application.

The output of any of the above methods may be a printed coded image (i.e., a combined main image and hidden secondary image printed on a document or other item), or may be a digitally coded image which is transmitted or stored for subsequent use .

Another method of embedding images is commonly used for banknotes and checks. In this method, a hidden image is created by changing the orientation of raster elements in the visible image at locations corresponding to content in the hidden image. For example, vertical raster lines in the main image may be changed to horizontal lines at locations corresponding to the hidden image. Typically, the hidden image can be viewed by tilting the note slightly. However, it is also possible to decode deviations in the main image with an optical decoder. This is due to the fact that where there is no hidden content the raster lines of the main image will run the length of the decoder's lens lines, but where there is a hidden image there will only be a cross section. This difference makes the hidden image appear much brighter than is visible to the eye when viewed through a decoder.

The common thread of all the methods described above and the resulting coded images is that deviations from regularized periodic properties (eg spatial position, tone density, raster angle) are involved. These deviations are made apparent by using a lenticular decoding lens with a frequency corresponding to that of the regularized properties. The frequency of the characteristic can be made equal to the lens frequency, or can be equal to an even multiple of the lens frequency. Lenticular lenses are used for content masking, emphasizing deviations from regularized properties and combining them into auxiliary images.

Lenticular lenses can be used to decode both visually coded images whose content has been systematically scrambled and coded images embedded in the main image or background. However, there are situations where the use of a physical (ie, hardware) decoder is impractical or impossible. Accordingly, the present invention proposes a method for decoding digitally encoded images without the use of physical optical decoding devices. In particular, the invention proposes a method that can be incorporated into a software-based decoder capable of decoding digitally encoded images. Decoders of embodiments of the present invention may be adapted to decode any digitally encoded image, including unprinted digitally encoded images, and printed encoded images that have been scanned or converted to digital form by other means. A digitally encoded image can be a hidden image embedded in the background or main image, or it can be a visible image that has been systematically scrambled or manipulated.

Now, a method of decoding a digitally encoded image according to the present invention will be described. Unless otherwise stated, the coded images to be decoded refer to the main image, with auxiliary images embedded in such a way that they can be viewed (decoded) using a lenticular lens. The main image can be a blank image with no discernible content (eg, a gray box), or it can be an actual image with discernible content.

The methods of the present invention can be divided into two categories: (1) methods that require content information of the main image, auxiliary image, or both; and (2) methods that do not require prior knowledge of image content. Both types of methods require knowledge of the encoding parameters used to encode and embed the auxiliary image. Specifically, the line frequency and line angle used to encode the image must be known.

Fig. 7 shows steps in a method M100 according to an embodiment of the present invention that may be used to decode an encoded image when an unmodified main image is known or available. The method starts at S100. At S110, a digitized copy of the encoded image is obtained. The digitally encoded image may be a version of the encoded image as a direct output of the auto-encoding process. The digitally encoded image can be stored for later retrieval by the decoding processor, or it can be transmitted from the originator to the decoding processor. Those of ordinary skill in the art will appreciate that such digitally encoded images may never have been printed on a document, product, label, or other verifiable item. Since the encoded image is provided in its original, digital form, there is the smallest possible distortion that has been introduced into the encoded image that will affect the encoding process. However, the orientation of the coded image is known explicitly.

In an alternative to the above, the digitally encoded image may be obtained by scanning or copying an encoded image that has been printed on a document, product, label, or other verifiable item. If a digitally encoded image is obtained in this manner, steps must be taken to ensure careful control of the relative orientation of the encoded image (such as by controlling the orientation of the document relative to the scanning device), or to determine the relative orientation of the encoded image (such as by including in or near the encoded image that will allow the decoding process to ensure the correct orientation of the image for decoding).

At S120, a digital copy of the original main image used to generate the encoded image is obtained. In many instances, the digitized master image may be obtained from the encoding processor, or may be retrieved from a data store where the encoded image was generated. Alternatively, the main image may be obtained from the source used to provide the image to the encoding processor. At S130, the digitized master image is rasterized to generate a comparison image. This rasterization is achieved using the encoding parameters used to generate the encoded image. In particular, the main image is rasterized using the same raster angle and line frequency that the encoding processor used to generate the encoded image. In some instances, a copy of the main image received from the encoding processor or retrieved from the data store may have been rasterized using these parameters, possibly using these parameters. In this case, the previously rasterized main image is established as the comparison image.

It should be understood that if the main image happens to be a blank background image, the control image will be similar to that of FIG. 4 . Otherwise, the control image is essentially a variation of the digitally encoded image without the auxiliary image embedded therein.

At S140, a pixel-by-pixel comparison is performed from the control image and the digitally encoded image to create a difference image. The difference image may be a composite of tone values established for each pixel based on whether there is a difference between the comparison image and the encoded image for each pixel. For example, a pixel in which the content of the encoded image differs from a corresponding pixel in the control image may be assigned a "true" value, and the corresponding pixel in the difference image may be set to "1" (corresponding to white). Pixels where the content of the coded image is the same as the corresponding pixel in the control image are assigned a "false" value, and the corresponding pixel in the difference image is set to "0" (corresponding to black).

The resulting difference image is a reconstruction of the auxiliary image used with the main image to generate the encoded image. At S150, the quality of the difference image can be enhanced using known image enhancement methods, including but not limited to: median or low-pass filter, adaptive filter, morphological processing, and customer-designed image enhancement methods . At S160, the difference image may be displayed on the terminal screen for storage or printing. Those of ordinary skill in the art will appreciate that differential images may be displayed before, after or during any enhancement steps. At S170, the method ends.

The quality of encoded images produced using method M100 may be affected by the method by which the digitally encoded images were obtained. The highest fidelity is obtained when the coded image is the exact output of an automatic encoding process and the rasterized master image is used in the encoding process, when the coded image is obtained by digitizing or capturing a digital version of the coded image for printing with an image acquisition device, resulting in slightly lower fidelity. This is because printing and image acquisition (eg scanning) processes introduce dimensional distortions as well as hue and texture variations, which can affect decoding results. In addition, errors in the orientation of the coded image relative to the image acquisition device may cause the digitally coded image to be misaligned with the control image when compared. As noted above, these effects can be reduced by carefully controlling the image acquisition process and/or by including alignment keys in or near the encoded image when it is printed.

As used herein, the term "image acquisition device" refers to any device or system for capturing or generating digital images from printed images or objects. Image acquisition devices include, but are not limited to: scanners, digital cameras, systems with a combination of analog cameras and frame grabbers. The image acquisition device may be adapted to capture images using light in the visible or invisible part of the spectrum (eg UV and IR).

As mentioned above, method M100 requires the master image to be available. For many applications, this is impractical. Therefore, some methods of the present invention do not have this requirement. FIG. 8 shows the steps in the same method M200 for decoding encoded images as above, except that the control images are always rasterized with blank images (eg, rasterized gray boxes). The method starts at S200. At S210, a digitized copy of the encoded image is obtained. As in the previous method, this may be the original, unmodified digitally encoded image, or it may be a captured image from a document or other item on which the encoded image has been printed. At S220, a comparison image is created by rasterizing the blank image with a raster angle and frequency corresponding to the encoding parameters used to encode the encoded image. Then, at S230, a difference image is constructed. The difference image can be constructed using the same pixel-by-pixel differencing method used in the method shown in FIG. 7 . At S240, an enhancement technique may be applied to the differential image, and at S250, the image may be displayed. The method ends at S240.

If the main picture used to generate the coded picture is a blank picture, the coded picture resulting from method M200 will be exactly the same as that obtained using method M100 of FIG. 7 . However, if the main image actually contains visual information, the encoded image resulting from method M200 will appear significantly different from the decoded image generated using method M100. This is because in method M100 the main image is filtered out from the main image. Then, in method M200, the difference image will include elements of the auxiliary image and the main image. In the resulting decoded picture, the decoded auxiliary picture appears to be placed on top of the main picture. Depending on the content of the two images, this can make the auxiliary image more difficult to distinguish or interpret.

Some methods for decoding digitally encoded images according to the invention have been developed in a way that more closely simulates the action of a lenticular decoder. The lenticular lens allows the viewer to view linear samples of the acquired image at intervals determined by the frequency of the lenticular lens. The lens magnifies these samples and is inserted by human vision into sequential pictures. When oriented at an appropriate angle, this causes deviations from the main image characteristics with the same frequency to be sampled and amplified, and thus stand out from the main image. The role of the lens is essentially to combine periodic samples of the encoded image into the reconstruction of the auxiliary image.

FIG. 9 is a flowchart of a method M300 for decoding a digitally encoded image using a sampling method similar to that of a lenticular lens. The method starts at S300. At S310, a digitized copy of the encoded image is obtained. As with the previous method, this may be the original, unmodified digitally encoded image, or it may be a captured image derived from a document or other item on which the encoded image has been printed. At S320, a series of elongated rectangular image content samples are obtained from the digitally encoded image. The samples are obtained at a frequency corresponding to the line frequency used to encode and orient the encoded image and the encoding angle used to encode the encoded image. Figures 10 and 11 show how image content samples are obtained. FIG. 10 shows a schematic diagram of a digitally encoded image 310 and a single sample 322 . The sample 322 has a vertical axis 324 positioned at a decoding angle α relative to the horizontal axis of the encoded image 310 . Comparable samples 322 are acquired for the entire encoded image 310 at a frequency corresponding to the frequency used to encode the encoded image 310 . The sample width can be defined to match the actual sampling of the lenticular decoder, or it can be preset to a small fixed width.

At S330, the image content samples are combined to form a composite sample image, wherein each sample is maintained at the same relative position with respect to the other samples. FIG. 11 shows a composite sample image 320 formed from samples 322 derived from an encoded image 310 . As can be seen in the illustrative example of Figure 11, the composite sample image has gaps between samples. At S340, each image sample is expanded perpendicular to its longitudinal axis so that the gap is close to its neighboring samples. This simulates the magnification effect of a lenticular decoder. This extension can be achieved using any image resizing algorithm known in the art. The resulting overall composite image provides a reconstruction of the auxiliary image as well as elements of the main image. At S350 and S360, this image can be enhanced and/or displayed, as in the previous method. The method ends at S370.

Similar to the method M200 of FIG. 8 , the method M300 does not require the source image to be known in advance. Also similar to method M200, method M300 produces an encoded image, including some elements of the main image. However, the decoding results of method M300 are generally better than those of method M200 because this method favors suppression of the main picture elements to a higher degree.

The results of this method can be further improved by constructing one or more additional synthetic images from additional sets of samples taken at the same frequency and orientation, but with slight shifts from the original samples. Combining these composite images together helps to further suppress elements of the main image and/or enhance the perceived strength of the auxiliary image in the decoded image. This process can be described as: creating multiple layers of samples and utilizing different techniques known in the art for flattening multiple layers (e.g. or sequence of operations) to combine them. As an example of the value of additional composite images, it can be seen that in certain parts of the coded image, the raster lines of the main image can be so thick that they block or cover raster deviations caused by auxiliary image elements. Acquiring the second sample set at a smaller distance from this location may better reveal the local auxiliary image elements. Averaging the two sample groups improves the overall perception of the auxiliary image. In another example, averaging a larger number of sample groups and filtering them with a low-pass filter can produce a reconstruction of the main image, which can be used to further suppress the main image from the encoded image. It should be understood that there is no limit to the number of sample sets and composite sample images that can be used.

Method M300 is of particular value when decoding captured encoded images. It should be understood that the image acquisition process may cause size and tone variations, which may affect the encoding result. More specifically, the orientation of the encoded image relative to the image acquisition device may be highly variable. The results of either of the above methods can be improved by adding certain features to the image at encoding time. This may include markings at predetermined positions that allow orientation errors and distortions to be identified and corrected. An image density standard that allows correction of tone density can also be included.

It is also possible to improve the performance of various decoding methods by choosing the form and content of the auxiliary images. For example, this can involve using symbols such as black and white squares, barcodes and other symbols instead of plain text or image-based markup.

It should be appreciated that the decoding methods described above and digital image decoders constructed to implement them may be adapted to decode any encoded image that can be decoded using a lenticular decoder. Furthermore, any image that has been encoded according to regularized periodic changes in a separately encoded image (e.g., a visually "scrambled" image) or in the main image or background in which a hidden image is embedded can be encoded using the method and decoder of the present invention. Encoded image to decode. In some embodiments of the invention, the sensitivity of the decoding method far exceeds that of an optical decoder. This enables the generation and use of encoded images based on very small periodic variations that cannot be discerned by an optical decoder.

As discussed in the '962 and '943 applications, multiple auxiliary pictures can be encoded into a single encoded picture, each auxiliary picture encoded with a different set of encoding parameters. Any number of auxiliary images embedded in such a coded image may be decoded using the decoding methods described above. The method is simply repeated for each auxiliary image with its associated encoding parameters.

Additionally, as discussed in the '962 and '943 applications, encoded images may be generated for embedding in digital documents using some combination of encoding parameters, which may include user-supplied parameters, non-user-supplied parameters, or user-supplied parameters. Both supplied and non-user supplied parameters. In one embodiment, the coded image is based in part on information extracted from the document and can be embedded into the digital document. At any time thereafter, the encoded image (or decoded images) from the digital document can be extracted/decoded using software configured to perform one of the digital decoding methods described above. The information in the decoded image (or decoded images) can then be compared to that in the digital document to see if the document has been tampered with since it was secured. This comparison can be made manually by the document user (e.g., by displaying the encoded image on a monitor and visually comparing the information from the displayed image with the data in the digital document) or automatically (e.g., by using optical properties to identify The software extracts the text from the decoded image and matches this text to the appropriate part of the digital document).

A method M400 of securing and authenticating digital documents in this manner is shown in FIG. 12 . The method starts at S400 and at S410 information is extracted from a digital document to be protected. This information may include graphic images, text, or other markup, and/or may include explanations or summaries of portions of the document's content. This information can be identified and extracted manually or automatically. At S420, construct an encoding parameter set. The set of encoding parameters may be a combination of user-supplied and non-user-supplied parameters, and may include parameters derived from information extracted from the digital document. At S430, an auxiliary image to be encoded is established. This auxiliary image can be user-provided or non-user-provided. The auxiliary image may be based on or include some or all of the information extracted from the digital document. At S440 and S450, the auxiliary image is encoded and embedded into the digital document. It should be understood that, depending on the encoding method used, S440 and S450 may be performed as a single combined operation. In some approaches, encoded images can be created and stored or transmitted to a user for later incorporation into a digital document. It should be understood that multiple auxiliary images may be encoded and embedded in the digital document, each such image encoded based on its own set of encoding parameters. Each of the different encoded images may be formed from any combination of user-supplied and non-user-supplied images and encoding parameters.

The protected digital document can then be transmitted, stored, printed or otherwise manipulated. At any time after the encoded image has been incorporated into the digital document, the authenticity of the digital document can be checked using the verification portion of the method. At S460 and S470, the encoded image is extracted from the digital document and decoded. The encoded image may be decoded using any digital decoding method including the methods described above. In a preferred embodiment, a digital decoding method is incorporated into software for automatically extracting and decoding encoded images from digital documents. In certain embodiments, OCR or other optical recognition software may be used to interpret content and/or extract information from digital documents. At S480, information from the encoded image is compared with information extracted from the digital document being verified. If the information in the digital document being evaluated does not match the information gleaned from the encoded image, the user may be alerted that there has been an unauthorized change to the digital document or that the digital document is not authentic. The method ends at S495.

It should be appreciated that the verification portion of method M400 may be separate from the encoded image generation portion, and that verification operations may be performed on any digital document that is claimed to be authentic and unchanged. Different encoding and decoding operations can be performed as a combination of automatic and non-automatic functions. It should also be understood that the input to the verification portion of method M400 is not limited to raw digital documents; if the document is printed, photographed, or otherwise transformed, it can be digitized using an image acquisition device to recreate the digital document, and then, by The verification part of method M400 verifies it.

FIG. 13 shows a system 400 for authenticating digital documents, in which the encoding and embedding functions are performed by an encoder part 410 and the decoding and verification functions are performed by a verification part 430 . The encoder portion 410 may include an encoding module 412 and an embedding module 414 , either or both of which may be in communication with an encoding information database 440 . The encoding module 412 is adapted or programmed to generate an encoded image using a set of encoding parameters and an authentication image that may include or be derived from content extracted from the digital document. Some or all of this information may be received from an encoding interface module 450 adapted to provide an interface between a user or document processing module and the encoding portion 410 . Encoding module 412 may store encoding parameter sets and/or verification images in encoding information database 440 for later use in authenticating digital documents. Encoding module 412 may also store the encoded image in database 440 and/or return the encoded image to encoding interface module 450 . The encoding processor 412 may also provide the encoded image to an embedding module 414 adapted to embed the encoded image into a digital document or a portion of a digital document. The digital document with embedded images may then be returned to the encoding interface module 450 .

The decoding portion 430 may include a decoding module 432 and a verification module 434 , either or both of which may be in communication with an encoded information database 440 . The decoding module 432 is adapted to retrieve encoding parameters and/or verification images from the encoding information database, and execute the digital decoding method of the present invention to decode digitally encoded images using the encoding parameters. The decoding module 432 may also be adapted to receive a digital document to be authenticated and to extract an encoded image from the digital document. The digital document may be received from an authentication interface 460 suitable as an interface between the authentication requesting device and the authentication portion 430 . After decoding the encoded image, the encoding module 432 may return the decoded image to the verification interface and/or forward the decoded image to the verification module 434 . The verification module 434 is adapted to extract content from the decoded image, which may be compared with verification criteria or with content extracted directly from the digital document. The verification module 434 may be adapted to retrieve such digital document content or may be adapted to extract it from a digital document. The verification module 434 may also be adapted to determine a verification result and return the result to the verification interface. Verification module 434 may include OCR software or barcode interpretation software that may be used to extract information from decoded images and/or digital documents.

It should be understood that encoding module 412, embedding module 414, decoding module 432, verification module 434, encoding information database 440, encoding interface module 450, and verification interface module 460 may be distributed among one or more data processors. For example, all of these modules could be located on a single user data processor. Optionally, different components of system 400 may be distributed to multiple data processors in selective communication over network 420 .

FIG. 14 depicts an exemplary system 500 for validating digital documents in which various system functions are performed on a plurality of processors interconnected by a network. In this system, encoding functions are performed on encoding processor 512 that is part of encoding server 510 , and decoding functions are performed by decoding processor 532 that is part of authentication server 530 . Encoding processor 512 may be in selective communication with first user processor 550 over network 520 . Decode processor 532 may be in selective communication with second user processor 560 over network 520 . Both encoding processor 510 and verification server 530 are in communication with or have selective access to database 540 . This access may be via the same network 520 or a different network or via another communication link. It should be appreciated that in certain embodiments, a predetermined set of fixed encoding/decoding parameters may be used, and therefore there is no need to store these parameters in database 540 . It should also be understood that, in certain embodiments, encoding processor 512 and decoding processor 532 may be located on a single server. It should also be understood that different aspects of the encoding and decoding process may be further distributed among multiple processors, including combined encoding/decoding processors and user processors 550,560. In addition, the user processors 550 and 560, the encoding processor 512 and the decoding processor 532 can also be a single processor or a server or modules of individual processors connected through a local area network.

In a typical mode of operation, a user wishing to protect a digital document submits a request for an encoded image to the encoding server 510 through the first user processor 550 . The request may include some or all of the encoding parameters, and may include the authentication image to be encoded. In some embodiments, the request may also include some or all of the digital document itself. The encoding processor 512 generates an encoded image using encoding parameters based at least in part on information provided by the user in the request. The encoding parameters used to generate the encoded image may also include non-user-supplied information. Encoding processor 512 may store encoding parameters and/or verification images in database 540 for later use in verifying digital documents. Encoding processor 512 may also store the encoded image in database 540 and/or transmit the encoded image back to user processor 550 (or another user processor) for embedding into a digital document. Optionally, encoding processor 512 may embed the encoded image into a digital document or portion of a digital document, and then transmit the digital document to user processor 550 .

The digital document may then be printed, stored or transmitted to other processors, including a second user processor 560 . Document authenticity can be verified at any time, whether in digital or printed form. If the document is in digital form, it may be transmitted by user processor 560 to verification server 530 for verification. Decode processor 532 receives the verification request and retrieves relevant encoding parameters from database 540 . Then, the decoding processor 532 decodes the digitally encoded image using the encoding parameters and the digital decoding method. The verification server 530 may also include a verification processor 534 adapted to process the output of the decoding processor and compare it to criteria for verification. Typically, verification criteria are structured in such a way that material changes or unauthorized production can be identified, while changes due to reduced fidelity or due to the presence of primary image elements are ignored. Verification processor 534 may include OCR or barcode interpretation software that may be used to extract information from decoded encoded images. The verification processor 534 may also be adapted to extract information or indicia from the digital document for comparison with information or indicia extracted from the decoded encoded image.

If the document has been printed, the authenticity of the document can be verified using an optical decoder having characteristics corresponding to the encoding parameters used to generate the encoded image. Alternatively, the printed document may be captured using a scanner or other image acquisition device 562 to produce a captured digital image. The captured digital image may then be transmitted by user processor 560 to verification server 530 for verification. The captured digital image can then be authenticated using the decode processor 532 and the authentication processor 534 in the same manner as an unprinted digital document.

It should be understood that document protection by generating encoded images may be performed by the document author or some other user in the document management system. Protected documents can be stored in a database or immediately sent to other users via the Internet or Intranet (or other network). In some embodiments of the invention, software suitable for performing digital decoding of encoded images may reside on any user processor. This software will only be usable to decode encoded images if the encoding parameters are available to the user. If the recipient of the digital document has decoding software and has access to the encoding parameters, the recipient can use the decoding software to see if the document has been tampered with since it was secured. If the recipient prints the digital document, the document is protected by an encoded image that is printed with the document.

The use of a digital decoder (ie any form of digital data processor suitable for decoding digitally encoded images according to the method of the invention) eliminates the need to print the document in order to verify its authenticity or to verify that it has not been tampered with. Furthermore, since the document can be examined in its digital form, there is no need for an optical decoder to have the characteristics to match the encoding parameters of the encoded images in the document. A system applying a combination of digital and optical decoders enables verification of the same document in both digital and printed form, thus crossing the digital-to-paper boundary.

A digital decoder may be any data processor having software for implementing one or more of the digital decoding methods of the present invention. A digital decoder may also be or include a hardware implementation of one or more decoding methods. For example, such hardware may include a digital signal processor (DSP) or other programmable device, or a series of hardware components suitable for carrying out the sequence of operations described above.

As mentioned above, a digital decoder can be used to extract and decode digitally encoded images from unprinted electronic documents or printed/captured documents. In some embodiments, a digital decoder can also be used to extract and decode encoded images embedded in holograms and diffraction gratings.

Therefore, another aspect of the present invention provides a security product that makes the transition of documents from digital to paper form more secure. This product may be referred to as a coded image exchange (or conversion) module. This security feature changes the set of encoding parameters used for document protection on the fly when the document is printed. The coded image exchange module is adapted to implement a method of exchanging encoding parameters for encoding an image. A method M500 according to one embodiment is shown in FIG. 15 . The method starts at S500 and at S510 a first encoded image is received. The image is encoded using a first set of encoding parameters. The first encoded image may be a newly generated encoded image received directly from the encoding processor, a previously generated encoded image retrieved from memory, or an extracted image derived from a digital document. In some examples, a first coded image may have been embedded in a digital document to preserve the document in an unprinted state, but the user wishes to change the coded image before printing.

At S520, regardless of its signal source, the first coded image is decoded using a digital decoder. Then, at S530, specific markers or parts of the image may be extracted from the decoded image. Then, at S540, re-encode part or all of the decoded images or information extracted from the decoded images by using the second encoding parameter set. Then, at S550, the encoded image generated using the second encoding parameter set is embedded in the digital document. If the original encoded image is extracted from a digital document, a second encoded image may be back-embedded into the same digital document as a replacement for the original encoded image. At S560, the digital document is stored and/or printed. When the digital document is printed, it will include a second version of the encoded image. The method ends at S595.

In some embodiments, the recoding operation S520 of the protection enhancement method M500 may be performed immediately before printing the digital document. As a result, unauthorized printing of a previously intercepted or appropriate version of an electronic document will produce a copy of the document that includes the first encoded image but does not include the second encoded image. Thus, subsequent verification of an unauthorized copy will reveal its forgery nature. It can be seen that multiple applications of the operations of method M500 at different stages of document generation and transmission can be used to determine where a digital document has been misappropriated.

The two encoding parameter sets used in method M500 can be made mutually exclusive. For example, parameter sets may be structured in such a way that if the image is printed and a digital decoder (operated with a first encoding parameter set) cannot decode a second encoded image encoded with a second parameter set, then it is configured to decode the second An optical decoder encoding an image (after the digital document has been printed) will not be able to decode an image encoded with the first parameter set. Optionally, a user of the digital encoder may be provided with access to the first and second sets of encoding parameters. In this case, the digital decoder can be used to decode the first and second coded images, while the optical decoder is limited to decoding the second coded image only.

In certain embodiments of the protection enhancement method M500, the first coded image may include elements of other security enhancement measures, such as digital watermarks or barcodes. For example, the first encoded image may include a barcode or watermark, which may itself be decoded using barcode or watermark recognition and/or interpretation software and the first set of encoding parameters. Then, the decoded image can be encoded for the second time by using the second encoding parameter set as described above. This embodiment can be extended further if the first coded image is formed as a lens decodable image of a barcode or watermark. The first encoded image can be decoded using the first set of encoding parameters to obtain a barcode or watermark, which can then be decoded using barcode recognition and/or interpretation software and the second set of encoding parameters. The decoded information may then be re-encoded using one or more additional encoding parameter sets.

Coded image exchange creates a security barrier at the point of digital-to-paper document transition. Only users with suitable coded image exchange software can produce printed documents that can be verified by corresponding optical decoders. Suppose a hacker breaks into a database of digital documents and downloads and prints them. Since the hacker does not have the encoded image exchange software, the encoded image will not be re-encoded before printing. Therefore, the document cannot be verified with the corresponding optical decoder. The barrier can be set to work in other ways: if someone scans a printed document to convert it to a digital format, or uses text editing software to create a fake document and inserts a captured coded image into it, then Digital decoders will not be able to decode captured encoded images.

The coded image exchange module can also be used for more complex authorization policies within document management systems. For example, all users with a digital decoding module can examine documents in digital form, but only authorized users with an encoded image exchange module can produce printed copies decoded by an appropriate optical decoder, thus revealing that the A specific copy of the document is printed. This level of control becomes especially important if a digital document must be approved by multiple users before it can be published, or if the document is unique and only one copy must be published, or if each paper copy of the document has monetary value.

In a variant of the image exchange method, the coded image can be made readable by a digital decoder and an optical decoder, while a second coded image is encoded by means of a coded image exchange module. This can utilize digital decoders or optical decoders to enable tracking of the source of documents detected as counterfeit.

It should be understood that instead of using an optical decoder a combination of image capture device and digital decoder could be used. In this case, the digital decoder used to verify the capture and re-digitally print the document may be preset to use a second set of encoding parameters, matching that used by the encoded image exchange module.

In some applications, multi-level encodings can be generated using previously described encoding methods. This can be achieved by encoding the encoded image a second time. For example, an encoded image may be formed from a first auxiliary image and a first main image. This encoded image is then used as a second auxiliary image, which can be used together with the second main image to form a second encoded image. The second encoded image may be generated using a different set of encoding parameters or even a different encoding method. This process can be repeated any number of times, thus creating multi-level encoding.

If an optical decoder is used to decode the hidden information, the superlative auxiliary image will be revealed by using a decoder that matches the final encoding process. Then another decoder can be placed on top of it to reveal the auxiliary image from the previous level, and so on.

As an alternative to using multiple optical decoders, the digital decoder of the present invention can be used to decode multi-level encoded images by simply applying and reapplying decoding steps using appropriate encoding parameters. The digital decoder of the present invention is particularly suitable for this purpose because of its sensitivity, flexibility and ease of use. For example, in a software-based decoder, the encoding parameters used can be easily adjusted and can be easily controlled so that unauthorized decoding of certain encoded image levels can be prevented.

In another approach to multi-level encoding, the optical image encoding process described above can be combined with other image concealment or masking methods. For example, a digital image including a digital watermark or barcode may be used as an auxiliary image, which is then encoded using one of the optical encoding methods described above (or other methods for producing an image decodable using a lenticular lens). Optionally, the encoded image can be used in a digital watermark or embedded in a barcode image. Furthermore, the digital decoder of the present invention can provide significant advantages for decoding levels of the coding hierarchy.

Those of ordinary skill in the art will readily appreciate that the present invention allows for a wide variety of uses and applications. Many other embodiments and improvements of the invention, and many variations, modifications and equivalent arrangements, in addition to those described herein, will be apparent from or reasonably suggested by the invention and its foregoing description, and without departing from the spirit or scope of the invention.

The method for protecting documents according to the present invention should not be confused with the system for encrypting emails and digital documents. Encryption makes the entire document unreadable by unauthorized users or interceptors. In contrast, the method of the present invention involves encoding and embedding images for preventing tampering of documents but does not involve obscuring document content. It is also possible to encrypt and decrypt digital documents (ie, documents having encoded images embedded therein) protected using the method of the present invention without affecting the tamper protection provided by the present invention. This provides additional protection levels that allow users to create complex multi-level protection systems. In these systems, encryption will prevent unauthorized viewing or interception during electronic transmission, while the use of encoded images will prevent tampering and forgery of document content.

While exemplary embodiments of the present invention have been shown and described above, it should be understood that the invention is not limited to the structures described herein. The present invention can be embodied in other specific forms without departing from its spirit and essential attributes.

Claims (32)

1, a kind of method of utilizing the coded image that at least one coding parameter decodes and produced by master image and at least one assistant images, form described coded image in such a way: when printing described coded image, if do not have the optical decoder equipment with described at least one coding parameter corresponding characteristic, then the beholder can't distinguish described assistant images; Described method comprises:

Obtain the digital version of described coded image;

Determine described at least one coding parameter; And

Utilize described at least one coding parameter, make up decoded picture according to described digital coding image.

2, the method that coded image is decoded of being used for according to claim 1 is characterized in that the action that makes up decoded picture comprises:

Rasterisation contrast image has the rasterisation frequency that obtains and the rasterisation contrast image of direction with generation from described at least one coding parameter;

Each pixel of described coded image and the respective pixel in the described rasterisation contrast image are compared, to discern those coded image pixels that its content is different from the content of corresponding rasterisation contrast image pixel;

The described coded image pixel of utilizing its content to be different from the content of corresponding rasterisation contrast image pixel makes up difference images; And

Form described decoded picture according to described difference images.

3, the method that coded image is decoded of being used for according to claim 2 is characterized in that described contrast image is a blank image.

4, the method that coded image is decoded of being used for according to claim 2 is characterized in that described contrast image is the digital version of described master image.

5, the method that coded image is decoded of being used for according to claim 1 is characterized in that the action that makes up decoded picture comprises:

Obtain first group of regularization periodic samples of described coded image, obtain shape, direction and the frequency of these samples according to described at least one coding parameter;

Make up the first synthetic sample image according to described first group of regularization periodic samples; And

Expand the sample of described first group of regularization periodic samples, to fill the space between the sample and to form first decoded picture.

6, the method that coded image is decoded of being used for according to claim 5, it is characterized in that each regularization periodic samples is the elongated rectangle section with longitudinal midline axle, and the frequency of described sample is corresponding to the coding frequency that is used for coded image is encoded, and the angle direction of described longitudinal midline axle is corresponding to the coding angle that is used for coded image is encoded.

7, the method that coded image is decoded of being used for according to claim 5 is characterized in that the action that makes up decoded picture also comprises:

Obtain second group of regularization periodic samples of described coded image, except described second group of regularization periodic samples with the predetermined part in cycle between the sample, depart from described first group of regularization periodic samples, the shape of these samples, direction and frequency are identical with described first group of regularization periodic samples;

Make up the second synthetic sample image according to described regularization periodic samples; And

Expand the sample of described second group of regularization periodic samples, to fill the space between the sample and to form second decoded picture.

8, the method that coded image is decoded of being used for according to claim 7 is characterized in that the action that makes up decoded picture also comprises:

By forming described decoded picture to described first and second decoded picture applied layers leveling operation.

9, the method that coded image is decoded of being used for according to claim 8, it is characterized in that described layer leveling operation comprises implements in the following action at least one to first and second decoded pictures, and described action comprises: decompose, multiply each other, average, overlapping, ask difference and repel.

10, the method that coded image is decoded of being used for according to claim 1 is characterized in that also comprising:

Utilization is handled one or more groups that constitutes by medium filtering, low-pass filtering, adapting to image filtering and form, strengthens the quality of described coded image.

11, the method that coded image is decoded of being used for according to claim 1, the action that it is characterized in that obtaining the digital version of described coded image comprises:

The digital version of the described coded image of retrieval from data-carrier store.

12, the method that coded image is decoded of being used for according to claim 1, the action that it is characterized in that obtaining the digital version of described coded image comprises:

Receive the digital version of described coded image from encode processor.

13, the method that coded image is decoded of being used for according to claim 1, the action that it is characterized in that obtaining the digital version of described coded image comprises:

Use image acquisition equipment, catch the digital version of described coded image from the previous printing edition of described coded image.

14, the method that coded image is decoded of being used for according to claim 13, it is characterized in that described image acquisition equipment be by optical scanner, digital camera and comprise analog camera and group that the system of frame grabber constitutes in one.

15, the method that coded image is decoded of being used for according to claim 1 is characterized in that the action of determining described at least one coding parameter comprises:

Described at least one coding parameter of retrieval from described database.

16, the method that coded image is decoded of being used for according to claim 1 is characterized in that the action of determining described at least one coding parameter comprises:

Receive described at least one coding parameter from encode processor.

17, a kind ofly be used to verify wherein the method for the digital document of embedded coding image, utilized a plurality of coding parameters and the checking content extracted has made up described coded image from described digital document; Described method comprises:

From described digital document, extract described coded image;

Utilize described coding parameter, described coded image is carried out digital decoding to produce decoded picture;

From described decoded picture, extract the decoded picture content; And

Described decoded picture information and the checking content of being extracted are compared.

18, method according to claim 17 is characterized in that described checking content comprises authentication image.

19, method according to claim 17 is characterized in that described checking content comprises the document exclusive data, and described document exclusive data is unique in fact for described digital document.

20, method according to claim 17 is characterized in that described decoded picture content and the action that the checking content of being extracted compares are comprised:

Determine whether the decoded picture content of being extracted is complementary with described checking content.

21, method according to claim 17 is characterized in that described checking content is stored in the database, and described decoded picture content and the action that the checking content of being extracted compares are comprised:

The described checking content of retrieval from described database.

22, method according to claim 17 is characterized in that described decoded picture content and the action that the checking content of being extracted compares are comprised:

From described digital document, extract described checking content.

23, a kind of system that is used to verify digital document comprises:

Coding module is suitable for making up coded image to be embedded in the digital document, utilizes at least one coding parameter and the checking content extracted from described digital document makes up described coded image;

Merge module is communicated by letter with coding module, and described merge module is suitable for described coded image is embedded in the described digital document;

Encoded information database, with described coding module selective communication, described database is suitable for storing at least one coding parameter;

Decoder module, with described encoded information database selective communication, described decoder module is suitable for:

Receive described digital document,

Described at least one coding parameter of retrieval from described database,

From described digital document, extract described coded image,

Utilize described at least one coding parameter, described coded image is carried out digital decoding with the generation decoded picture, and

From described decoded picture, extract the decoded picture content;

Authentication module is communicated by letter with described decoder module, and described authentication module is suitable for described decoded picture information and the checking content of being extracted are compared.

24, system according to claim 23, it is characterized in that described system comprises user data processor, described user data processor comprises the addressable port module, described addressable port module and described coding module selective communication, and be suitable for asking coded image is embedded in the described digital document.

25, system according to claim 24, one or more groups that it is characterized in that being made of described coding module, merge module, encoded information database is the part of described user data processor.

26, system according to claim 23, it is characterized in that described system comprises authentication server, described authentication server is communicated by letter with at least one user data processor by network, described decoder module and described authentication module are the parts of described authentication server, and described authentication server is suitable for receiving confirmation of secretarial document request from described at least one user data processor, and will verify that the result turns back to described at least one user data processor.

27, a kind of method that is used to strengthen to the protection of the digital document that wherein embedded first coded image has utilized the checking content group and the first coding parameter group to make up described first coded image; Described method comprises:

Utilize the described first coding parameter group that described first coded image is carried out digital decoding to produce decoded picture;

From described decoded picture, extract described checking content group; And

Utilize the described checking content group and the second coding parameter group to make up second coded image.

28, method according to claim 27 is characterized in that described checking content comprises data unique in fact for described digital document.

29, method according to claim 27 is characterized in that also comprising:

From described digital document, extract described first coded image.

30, method according to claim 27 is characterized in that also comprising:

Described second coded image is embedded in the described digital document.

31, method according to claim 28 is characterized in that also comprising:

Printing has the described digital document of embedding described second coded image wherein.

32, method according to claim 31 is characterized in that also comprising:

But receive identifying file verifying, but described identifying file has the embedding coded image verified wherein; And

By utilizing the described second coding parameter group to attempt can verifying that coded image decodes, but identifying file is verified.

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