HK1139901B - Methods and apparatuses for creating authenticatable printed articles and subsequently verifying them - Google Patents

Description

Apparatus for creating authenticatable printed articles and subsequently authenticating them

The divisional application is a divisional application based on the chinese patent application having the title "method and apparatus for creating authenticatable printed articles and then authenticating them" with the application number of 200580013900.9, the application date of 09/03/2005.

Technical Field

The present invention relates to security methods and in particular to verifying the authenticity of a printed document or other printed article, such as a personal Identification (ID) card, a cardboard packaging product or a unique document, such as a bill of lading or a document with an initial signature, seal or indicia.

Background

Many conventional authentication security systems rely on processes that are difficult to perform for anyone other than the manufacturer, where the difficulty is imposed by the expense of fixtures, the complexity of technical expertise, or both. Examples are the provision of watermarks in banknotes and holograms in credit cards or passports. Unfortunately, criminals are becoming more sophisticated and can in fact reproduce everything original manufacturers can do.

Thus, there are known methods for verifying security systems that rely on creating security tokens using some process governed by laws of nature that result in each token being unique and, more importantly, each token having a measurable unique characteristic and thus being able to serve as a basis for subsequent verification. According to the method, the marking is manufactured and measured in a set method that obtains unique characteristics. The characteristics may then be stored in a computer database or retained. Such a marking can be embedded in a carrier article, such as a banknote, a passport, an ID card, an important document. Subsequently, the carrier article may be measured again and the measured characteristic compared to the characteristics stored in the database to determine whether there is a match.

Within this general approach, it has been suggested to use different physical effects. One effect that has been considered is to measure the magnetic response characteristics from the deposited magnetic material, where each sample has a unique magnetic response as a result of naturally occurring defects in the magnetic material that is formed in an irreproducible manner [1 ]. Another effect considered in many prior art documents is the use of laser speckle from inherent properties of the article to provide unique characteristics.

GB 2221870A [2] discloses a method in which a security device, such as an ID card, effectively has a tag embossed thereon. The marks are in the form of structured surfaces derived from a master. The speckle pattern from the light scattering structure is unique to the master and can therefore be measured to prove the authenticity of the mark on the security device. In a reader having a laser for generating a coherent beam of light roughly equal in size to the mark (2mm diameter) and a detector, such as a charge-coupled device (CCD) detector, for measuring the speckle pattern produced by the interaction of the laser beam and the mark, the mark on the security device is measured. The resulting data is recorded. For verification, the security device may be placed in the reader and its recorded speckle pattern signal compared again with a similar recorded signal from a reference device generated from the same master.

US 6,584,213[3] describes a further alternative to the use of speckle patterns reflected from specially tailored surface structures, in which speckle patterns are used in transmission from specially tailored transparent signs. A preferred implementation of this technique is to customize the epoxy logo to a size of about 1cm x 1cm with glass spheres embedded therein. The marking is customized by mixing glass spheres in a colloidal suspension in a fluid polymer and then curing to fix the position of the glass spheres. A unique set of glass spheres is detected using a transmitted coherent laser beam by a CCD detector positioned to measure the speckle pattern. In a modification of this method, the known identifier is encoded on a reflective surface which is then glued to one side of the sign. The probe light passes through the mark, reflects off of the known identifier, and then passes through the mark again. The glass spheres thus change the speckle pattern so that a unique hash key is generated from the known identifier.

Kralovic [4] simply reported that in the eighties, workers at the Sandia national laboratory of US performed special banknote paper tests injected into cut optical fibers. The speckle pattern can be measured from the optical fibre and a digital symbol version printed as a barcode on the side of the banknote. However, kralovic reports that this idea does not work properly because the fiber is too fragile and the speckle pattern changes rapidly due to wear as the banknote is circulated. This means that the speckle pattern measured from the optical fibre used in the banknote no longer matches the barcode, so that the banknote can no longer be verified in the intended manner by the speckle pattern.

Anderson [5] also briefly speaks at page 251 of its 2001 textbook, a scheme that appears similar to that described by Kravolec [4], for monitoring weapon control agreements. Anderson observed that many materials have unique surfaces, or that such surfaces can be made by eroding them with small amounts of explosive. That is, it makes it easy to identify stationary equipment, such as heavy cannons, where identifying each barrel is sufficient to prevent cheating weapon control agreements by either party. Anderson reports use laser speckle technology to measure the surface map of the barrel, either recorded in a log or affixed to the device, as a machine-readable digital signature.

Instead of using laser speckle, there is a more direct set of suggested solutions that simply image an item with high resolution and use this high resolution image as a unique feature, which can then be re-imaged for verification of authenticity. This can be viewed as employing conventional methods for fingerprint repositories held by the police.

US 5,521,984[6] suggests the use of an optical microscope to obtain images of small areas of expensive items, such as paintings, engravings, stamps, gems or special documents.

Anderson [5] reported on page 252 of his 2001 textbook that the postal system is considering this approach based on directly imaging envelopes with a microscope. The image of the paper fibers that produced the envelope is reported, the pattern extracted and recorded in the digitally marked postal indicium.

US 5,325,167[7] suggests imaging the particle structure of toner particles on a part of an expensive document according to a similar scheme.

With this prior work, there are various desirable characteristics that are evident from the ideal authentication scheme.

The reported magnetic or speckle based techniques seem to offer a high level of security, but for specific implementations special materials [1, 2, 3] need to be tailored to ensure long-term stability of the probe structure [4 ]. In many cases, it is not practical to integrate the tag into the item to be secured. In particular, integrating a resin label or a magnetic chip in paper or cardboard is not easy and involves considerable expense. For integration with paper or cardboard, any sign should ideally be printable. In addition, there is an inherent security risk of the method based on the affixable labels, as the labels may be removed and affixed to different items.

The reported direct imaging techniques [5, 6, 7] have the advantage that they obtain their digital signature directly from the article, avoiding the need for special signs. However, their intrinsic safety is low. For example, they are susceptible to fraudulent access to stored image data, allow for the production of items that can be incorrectly verified as authentic, or be counterfeited by simply using a high-resolution printer to print an image that is seen under a microscope when viewing the relevant portion of an authentic item. The security level of direct imaging techniques is also proportional to the amount of imaging data, necessitating the use of expensive high resolution imaging devices for higher security levels. This is acceptable in some applications, such as postal sorting or banknote validation, but is not acceptable in many applications.

Disclosure of Invention

The present invention provides a new system that can generate verifiable documents or other printable items, and that can be verified later without difficulty and with a high level of security. A printer with an integrated scanner is provided for obtaining a digital signature from paper or other articles when printed. An integrated scanner illuminates an article and collects data points from coherent light scattered from many different parts of the article as it is printed, so as to collect a large number of independent data points, typically 500 or more. A digital signature derived from the data points is stored in a database, with an image printed on the article. Later, the authenticity of the article declared to be the original printed article may be verified by scanning the authentic article of the declaration to obtain a digital signature thereof. The database is then searched to determine if a match exists. If a match is found, the image stored in the database with the matching digital signature is displayed to the user to allow further visual verification of the authenticity of the item. The image is displayed along with other relevant literature data relating to the item. This provides a highly secure system that also includes human verification of the manner in which a visual comparison is made between the document or other printed article being inspected and the document or other printed article displayed on the display.

In this way, each item printed can be automatically scanned and its digital signature recorded in the database along with the item's image file, using the printer normally. Each print item can be verified later as to whether it is authentic or not. For example, originals can be easily distinguished from copied or counterfeited pieces because the digital signature is unique to the printed substrate, e.g., the paper that is printed on it.

Various aspects of the present invention relate to a printing device with an integrated scanner, means for creating authenticatable articles that can be used with the printing device, and means for later verifying the authenticity of an article that is represented as authentic or for which verification of authenticity is desired. A corresponding method of creating a verifiable item and verifying the authenticity of the item constitutes a further aspect of the present invention.

The present invention provides, in one aspect, a printing apparatus comprising: a print head for printing on an article; a feed mechanism for conveying the article past the print head; and a scanning head comprising a coherent source and a detector arrangement, wherein the coherent source is arranged to direct light at the article conveyed by the feed mechanism, and the detector arrangement is arranged to collect a set of data points from signals obtained as the light scans over the article, wherein different data points relate to scatter from different parts of the article.

The present invention provides in another aspect an apparatus for creating an authenticatable article, comprising: a printer driver to create an instruction for the printing device to print an image; a data acquisition interface for receiving a set of data points from a signal obtained by scanning coherent light over an article during printing, wherein different data points relate to scattering of the coherent light from different parts of the article; and a processor to determine a digital signature of the item from the set of data points and create a record in a database, wherein the record includes the digital signature and a representation of the image.

The present invention provides in another aspect an apparatus for verifying the authenticity of an article, comprising: a scanning apparatus comprising a coherent source for scanning light over the article, and a detector arrangement configured to collect a set of data points from signals obtained when scanning the light, wherein different data points relate to scattering of the coherent light from different parts of the article; a processor for determining a digital signature of the item from the set of data points; a database comprising a plurality of records of previously scanned items, each record comprising a previously determined digital signature for that item and a visual representation of that item; and a signature verification module to search the database to determine if a match exists between the digital signature obtained by the scanning device and the digital signature stored in one of the records, and if a match is found, to display a visual representation of the item stored in the matched record.

Additionally, the user may be presented with confidence in the match, which indicates how well the digital signatures from the initial scan and rescan correspond. In this regard, it should be noted that even a rescanned digital signature from a real item does not exactly match its stored database copy. The test of match or mismatch is a similarity between the initial scan signature and the rescanned signature stored in the master database. It was found that typically a good quality match has about 75% bit agreement compared to an average of 50% agreement for a fraudulent match.

The database record may usefully include bibliographic data relating to the scanned item. In addition, when a match is found, the signature verification module will display the document data. For example, in the case of a document, the document data may include in the narrative text the summary and creation date of the document, a representation of the creator, and the printer ID of the printer used to create the document.

The present invention provides in another aspect a method of creating an authenticatable article, comprising: printing an image on an article; collecting a set of data points from signals obtained as the coherent light scatters from the article as the article scans the coherent light, wherein different data points relate to scatter from different parts of the article; determining a digital signature of the item from the set of data points; and creating a record in a database, wherein the record includes the digital signature and a representation of the image.

The present invention also provides another method of creating an authenticatable article, comprising: scanning the coherent light over the article and collecting a set of data points from signals obtained when the coherent light scatters from the article, wherein different data points relate to scatter from different parts of the article; determining a digital signature of the item from the set of data points; and printing an image on the article and encoding the digitally signed label according to a machine readable encoding protocol. Thus, the tag is a characteristic of the inherent structure of the article. In this case, the signature is preferably encoded in the tag using an asymmetric encryption algorithm. For example, the tag may represent a password that is decrypted by a public key in a public/private key encryption system. This is particularly convenient for many printable materials, particularly paper or cardboard, if the labels are ink labels applied with a printing process, preferably in the same process as the creation of the article, i.e. in the same process as the printing of the image onto the document. For example, an image may be printed on paper, and then the paper is again fed through the printer to print a signature encoding label thereon using a dual paper feed mechanism. The tag may be visible, such as a barcode, or invisible, such as when the article is a smart card, the tag is implemented as data in a smart chip.

Printing and scanning are conveniently performed as the article is conveyed past the print head and the scan head, respectively.

The present invention provides, in another aspect, a method of verifying the authenticity of an article, comprising: scanning the coherent light at the article and collecting a set of data points from signals obtained when the coherent light scatters from the article, wherein different data points relate to scatter from different parts of the article; determining a digital signature of the item from the set of data points; providing a database comprising a plurality of records for previously scanned items, each record comprising a digital signature previously determined for that item and a visual representation of that item; and searching the database to determine if there is a match between the digital signature obtained by the scanner and any of the digital signatures stored in the database, and if a match is found, displaying a visual representation of the item stored in the database.

It will be appreciated that the article may be made of paper or cardboard or any other printable substrate, having a surface suitable for providing a digital signature when scanned in the manner of the present invention. It will also be understood that reference to light should not be limited to visible electromagnetic radiation and includes, for example, infrared and ultraviolet radiation.

From the following examples, the invention is considered to be particularly suitable for paper or paper articles.

1. Documents of value, such as shared certificates, bills of goods, passports, intergovernmental treaties, ordinances, driver's licenses, certificates of vehicle performance, certificates of any authority

2. Any document used for tracking or tracing purposes, e.g. envelope of postal system, law enforcement tracked bank note

3. Package for products for sale

4. Label labels on designer goods, such as fashion items

5. Packaging for cosmetic, pharmaceutical or other products

6. Notarization and legal original documents

7. Identity cards and papers

For example, a selected batch of a particular type of printed item may be generated for tracking or tracing. A batch of banknotes can be printed, particularly to introduce a known crime circle, such as a payment lanyard or bribery or the purchase of contraband. These are identical to normal banknotes but are logged onto a database such that the database includes not only the unique digital signature of the banknote paper of each banknote but also the image of the banknote including its serial number.

It is contemplated that the present invention may identify any other printable substrate material as long as it has an appropriate surface structure. The type of material having a very smooth surface on the order of a microscopic scale may be inadequate. The appropriateness of the printed material can be readily determined by testing some representative sample.

In one set of embodiments, the data acquisition and processing module is configured to further analyze the data points to identify signal components that conform to a predetermined encoding protocol and to generate a reference signature therefrom. The characteristics of the predetermined encoding protocol are envisaged to be based on contrast, i.e. in most embodiments, scattering signal intensity. In particular, a conventional barcode protocol may be used, wherein, in the case of an ID barcode or a more complex pattern for a 2D barcode, the barcode is printed or applied to the article in the form of a bar. In this case, the data acquisition and processing module is used to perform a comparison to determine whether the reference signature matches a signature obtained by reading an item already located in the reading volume. Thus, an item, such as paper, may be marked for a digitally signed form, such as a barcode, having its own characteristics. The reference signature should be obtained from the property of the article with a one-way function, i.e. using an asymmetric encryption algorithm requiring a private key. This acts as a barrier to unauthorized third parties having readers who want to read counterfeit items and print on them a label representing the scanning of the reader according to an encryption scheme. Typically, a barcode label or other indicia will represent a password that can be decrypted by a public key, and a reserved private key will be used for authorized taggers.

The database may be part of a mass storage device forming part of the reader apparatus or may be located at a remote location and accessed by the reader via a telecommunications link. The telecommunications link may take any conventional form, including wireless and fixed links, and may be available over the internet. The data acquisition and processing module may be used, at least in some modes of operation, to add a signature to the database if no match is found. For obvious reasons, the tool will typically allow authorized individuals.

In addition to storing signatures, signatures in a database may also be used to associate signatures with other information about an item, such as scanned copies of documents, photographs of passport holders, details about the place and time of manufacture of a product, or details of an intended sales destination where goods may be sold (e.g., to track grey imports).

It is envisaged that the signature will in most applications be a digital signature. Typical sizes of digital signatures by current technology are in the range of 200 bits to 8k bits, and at present, it is preferable to have a digital signature of about 2k bits in size for high security.

The present invention also provides a printing apparatus comprising: a feed mechanism for conveying the article past the print head; a scanning head comprising a coherent source and a detector arrangement, wherein the coherent source is arranged to sequentially direct light onto each of a plurality of surface regions of an article conveyed by a feed mechanism, and the detector arrangement is arranged to collect a set comprising sets of data points from signals obtained when scanning light over the article, wherein different sets of data points relate to surface structure induced scattering from different respective surface regions of the article; and the print head to print an image on the article and encode a digitally signed label pattern of the article determined by the set of groups of data points according to a machine readable encoding protocol.

The present invention also provides an apparatus for creating an authenticatable article, comprising: a printer driver to create an instruction for the printing apparatus to print an image; a data acquisition interface for receiving a set comprising sets of data points from signals obtained by sequentially scanning light over each of a plurality of surface areas of the article during printing, wherein different sets of data points relate to scattering caused by surface structures from different respective surface areas of the article; and a processor for determining a digital signature of the item from the set of data point groups and determining a printable label pattern encoding the digital signature according to a machine-readable encoding protocol; wherein the printer driver is further operable to create instructions for the printing device to print a label design on the article.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made by way of example to the accompanying drawings, in which:

drawings

FIG. 1A is a perspective view of a scan head of an embodiment of the present invention, further showing a sheet of paper;

FIG. 1B is a side view of the scan head of FIG. 1A with paper;

FIG. 2 is a schematic perspective view of a paper showing how the paper is sampled n times over its scan area by scanning an elongated beam thereover;

FIG. 3 is a schematic block diagram of the functional components of a system for creating authenticatable items;

FIG. 4 is a perspective view of a printing apparatus with an integral scan head;

FIG. 5 schematically illustrates, in side view, another imaging device of a scanner embodying the present invention based on directed light collection and overlay illumination;

FIG. 6 schematically shows, in plan view, the optical footprint of another imaging device for a reader embodying the present invention, in which a directional detector is used in conjunction with localized illumination by an elongated beam;

FIG. 7 is a microscope image of a paper surface with an image covering an area of about 0.5X 0.2 mm;

FIG. 8A shows raw data from a single photodetector, including photodetector signals and encoder signals, using the scan head of FIG. 1A;

FIG. 8B shows the photodetector data of FIG. 8A after linearization and averaging of the amplitude with the encoder signal;

FIG. 8C shows the data of FIG. 8B after being digitized in accordance with the average level;

FIG. 9 is a flow chart showing how a digital signature of an article is generated by a scan;

FIG. 10 is a flow chart showing a printing process during which the paper being printed is scanned and its digital signature calculated and stored in a database;

FIG. 11 is a schematic side view of a reader device for scanning an item for authentication;

FIG. 12 is a schematic block diagram of functional components of the reader device and associated system components of FIG. 11;

fig. 13 is a perspective view of the reader device of fig. 11 showing an external appearance thereof;

FIG. 14 is a flow chart showing how the digital signature of an item obtained by a scan is verified against a database storing digital signatures of previously scanned items;

FIG. 15 is a flowchart showing the overall process of how a document is scanned and the results provided to a user for verification purposes;

FIG. 16 is a screen shot of a user interface displayed when the rescanned document is verified as authentic;

FIG. 17 is a schematic plan view of an ID card with a bar code label encoding a digital signature derived from inherently measured surface features;

FIG. 18 is a schematic plan view of an ID card with a chip encoding digitally signed data obtained from intrinsic measured surface properties; and

FIG. 19 is a schematic plan view of a warranty document having two barcode labels encoding digital signatures derived from intrinsic measured surface characteristics.

Detailed Description

Fig. 1A and 1B are schematic representations of perspective and side views, respectively, of a scan head 10 in accordance with an embodiment of the present invention. The scanner head 10 is used to measure a digital signature from a sheet of paper 5 or other printable item conveyed through the scanner head 10 in the x-direction through its reading volume (see axis of insertion in the figure). The main optical components are a laser source 14 for generating a coherent laser beam 15 and a detector arrangement 16 of k photodetector elements, where k is 4 in this example, denoted 16a, 16b, 16c and 16 d. The laser beam 15 is focused by a cylindrical lens 18 to an elongated focal point extending in the y-direction (perpendicular to the plane of the figure) and lying in the plane of the paper path. In an exemplary prototype, the elongated focal spot had a major axis dimension of about 2mm and a minor axis dimension of about 40 microns. These optical components are contained in the mounting block 11. In the embodiment shown, four detector elements 16a.. d are distributed at different angular offsets on either side of the beam axis in an interdigitated comb arrangement from the beam axis in order to collect light scattered in reflection from an item present in the reading volume. In the exemplary prototype, the offset angles were-70, -20, +30, and +50 degrees. Light access to the detector elements 16a.. 16d is provided through holes in the mounting block 11. The angles on either side of the beam are chosen so as to be unequal so that the data points they collect are as far as possible independent. All four detector elements are arranged in a common plane. When the coherent light beam is scattered from the paper 5, the photodetector elements 16a.. d detect light scattered from the surface of the paper 5 being conveyed past the scanning head 10. As shown, the source is mounted so that the beam axis of the laser beam 15 is in the z direction so as to strike the paper 5 at normal incidence.

It is generally desirable for the depth of focus to be large so that any difference in the z direction of paper positioning does not result in a significant change in the size of the beam incident on the paper. In the prototype shown, the depth of focus is about 0.5mm, large enough to produce good results. The parameters focal depth, numerical aperture and working distance are independent, resulting in a very well known trade-off between spot size and focal depth.

When the scan head 10 is integrated into another conventional printer, a paper feed mechanism will be used to linearly move the paper across the scan head 10 in the x-direction so that the beam 15 is scanned in a direction transverse to the long axis of the elongate focus. Since the coherent light beam 15 is dimensioned at its focal point so that the cross-section in the xz-plane (the plane of the figure) is much smaller than the projection of the reading volume in the plane perpendicular to the coherent light beam, i.e. the plane of the paper 5, the paper feeding mechanism will cause the coherent light beam 15 to sample many different parts of the paper.

Fig. 2 is included to illustrate the sampling and is a schematic perspective view showing how the read zone is sampled n times by scanning an elongated beam over it. The adjacent rectangles numbered 1 to n of the region of sampling length "1" and width "w" where "w" is the long dimension of the cylindrical focal point represent the sampling positions when the focused laser beam is swept across the paper by the paper feed. Data collection is performed to collect a signal at each of the n positions as the paper is conveyed past the scan head. Thus, a series of k × n data points relating to scattering from n different shown portions of the paper are collected. Typically, only a portion of the paper length will be sampled. For example, the length "l" may be about several centimeters.

With an exemplary minor dimension of the focus of 40 microns, and a scan length of 2cm in the x-direction, 2000 data points and k-4 are provided. Depending on the desired level of security, the type of article, the number of detector channels "k", and other factors, a typical range of values for k n is 100 < k n < 10,000. It has also been found that increasing the number k of detectors also improves the insensitivity of the measurement to surface degradation of the article by processing, printing, etc. Indeed, with the prototypes used so far, the rule of thumb is that the total number of independent data points, i.e. k × n, should be 500 or more in order to provide an acceptably high level of security with various surfaces.

FIG. 3 is a schematic block diagram of functional components of a system for creating authenticatable articles. The printer 22 is connected to a Personal Computer (PC)34 by a conventional connection 23. The detectors 16a.. d of the detector module 16 are connected by respective electrical connection lines 17a.. d to a digital-to-analog converter (ADC) which is part of a Programmable Interrupt Controller (PIC) 30. It will be appreciated that optical or wireless connections may also be used instead of or in combination with electrical connections. The PIC 30 is connected to a Personal Computer (PC)34 by a serial connection 32. The PC34 may be a desktop or laptop computer. As an alternative to a PC, other intelligent devices may be used, such as a Personal Digital Assistant (PDA) or a dedicated electronic unit. The PIC 30 and the PC34 together form a data acquisition and processing module 36 for determining a signature of the article from the collection of data points collected by the detectors 16a. The PC34 accesses a database (dB)40 via an interface connection 38. The database 40 may reside in memory on the PC34 or stored on a drive thereof. In addition, the database 40 may be remote from the PC34 and accessed via wireless communication, such as using a mobile telephone service or a wireless Local Area Network (LAN), in conjunction with the internet. In addition, the database 40 may be stored locally on the PC34, but downloaded periodically from a remote source.

The database 40 is used to compile a digital signature library. The PC34 is programmed to obtain, in use, scan data from the detector 16a.. d each time a document is printed out by the printer 22, and to calculate a digital signature from the data. Then, a new record is created in the database 40, containing the digital signature, the image file that has been printed on the paper, and the document data relating to the document.

Fig. 4 is a perspective view of a printer 22 having the above-described scanning head 10 integrated therein. The printer 22 is a conventional printer except for the scan head and associated electronics. To schematically show the paper feeding mechanism, the final roller pair 9 thereof is shown. It will be appreciated that the paper feeding mechanism includes additional rollers and other mechanical components. In the prototype that has been built, the scan head is intended to be conveniently mounted directly after the final roll of paper, as shown. It will be appreciated that the scanning head may be mounted at many different locations along the transport path of the paper. Further, although a laser printer is illustrated, it will be appreciated that any type of printing device can be used. As well as other forms of printers, such as inkjet printers or thermal printers, the printing device can be any other type of printing device not traditionally considered a printer, such as a networked photocopier or industrial printer. For example, the printing device can be a printer for printing banknotes, checks or travelers checks.

The above embodiments are based on locally exciting a coherent light beam of small cross-section in combination with a detector that accepts light signals scattered over a larger area including a local excitation region. Functionally equivalent optical systems can be designed based on directional detectors that collect light from only a localized area, combined with excitation of a larger area.

Fig. 5 schematically shows, in a side view, an imaging device for a reader embodying the invention based on directional light collection and overlay illumination of a coherent light beam. The array detectors 48 are arranged in conjunction with the cylindrical microlens array 46 such that adjacent swaths of the detector array 48 collect light only from corresponding adjacent swaths along the paper 5. Referring to fig. 2, each cylindrical microlens is arranged to collect an optical signal from one of the n sampling bars. Coherent illumination may then occur by blanket illumination of the entire sampled area (not shown in the figure).

In some cases, a hybrid system that combines local excitation and local detection is also useful.

Fig. 6 schematically shows in plan view the optical footprint of such a hybrid imaging device for a reader embodying the present invention, in which a directional detector is used in conjunction with the local illumination of an elongate light beam. This embodiment can be seen as a modification of the embodiment of fig. 1A and 1B, wherein a directional detector is provided. In this embodiment, three sets of directional detectors are provided, each set for collecting light from a different part along the "1 xw" excitation spring. The collection area from the plane of the reading volume is shown by the dashed circle, so that a first set, e.g. 2, of detectors collects the light signal from the upper part of the spring, a second set of detectors collects the light signal from the middle part of the spring, and a third set of detectors collects the light signal from the lower part of the spring. Each set of detectors shown has a circular collection region of about 1/m in diameter, where m is the number of subdivisions of the excitation spring, where m is 3 in this example. In this way, the number of independent data points can be increased by a factor of m for a given scan length of 1. One or more different sets of directional detectors may be used for purposes other than collecting the optical signal of the sampled speckle pattern, as described below. For example, in the case of a printed barcode, a set of light signals may be used that are collected in a manner suitable for barcode scanning, for example to encode some aspect of a document, such as its bibliographic data. If this is the case, it is sufficient that the group contains only one detector, since the advantages of the cross-correlation will not be obtained when only scanning is used for the comparison.

Now describing the principle structural and functional components of various reader devices suitable for carrying out the present invention, numerical processing for determining a digital signature is now described. It will be appreciated that this numerical processing is implemented mostly with a computer program running on the PC34 and some elements subordinate to the PIC 30.

Fig. 7 is a microscope image of the paper surface covering an area of about 0.5 x 0.2 mm. The figure is included to illustrate that macroscopically flat surfaces, such as from paper, are in many cases highly structured on a macroscopic scale. For paper, the surface is macroscopically highly structured as a result of the interwoven network of wood fibers that make up the paper. The figure also illustrates a characteristic length scale for wood fibers of about 10 microns. This dimension has the correct relationship to the wavelength of the light of the coherent light beam to produce diffraction, thereby producing speckle, and also diffuse scattering with a profile according to the fiber direction. It will thus be appreciated that if the scanning head is designed for a particular class of printable substrate material, the wavelength of the laser light may be adapted to the size of the structural features of the class of materials to be scanned. It is clear from this figure that the local surface structure of each sheet of paper will be unique, depending on how the individual wood fibres are arranged. A sheet of paper is thus indistinguishable from specially created marks, such as the special resin marks or magnetic material deposits of the prior art, in that it has a unique structure as a result of a manufacturing process governed by laws of nature. The same applies to many other types of articles.

In other words, the inventors have found that when unique characteristics can be measured in a straightforward manner from a variety of everyday items, it makes no sense at all to try and spend money to make a specifically tailored logo. Now, data collection and numerical processing of the scattered signal using the natural structure of the surface (inside in the case of transmission) of the article is described.

Fig. 8A represents raw data from a single one of the photodetectors 16a.. d of the reader of fig. 1A. The graph plots signal strength and number of points n (see fig. 2) in arbitrary units (a.u.). The higher trace that fluctuates between I-0-250 is the raw signal data from the photodetector 16a. The lower trace is the encoder signal picked up from the marker 28 (see fig. 2), which is near I-50.

FIG. 8B shows the photodetector data of FIG. 8A after linearization by the encoder signal (note that although the x-axis is not as critical, it is not the same scale as FIG. 8A). In addition, the average of the intensities is calculated and subtracted from the intensity values. The data values thus processed fluctuate above and below 0.

FIG. 8C shows the data of FIG. 8B after digitization. The digitization scheme employed is a simple binary scheme, where either positive intensity value is set at a value of 1 and either negative intensity value is set at 0. It will be appreciated that multi-state digitization could also be used, or any of a number of other possible digitization methods. The most important feature of digitization is simply that the same digitization scheme is consistently employed.

FIG. 9 is a flow chart showing how a signature of an item is generated by scanning.

Step S1 is a data acquisition step during which the optical intensity at each photodetector is obtained every approximately 1ms over the entire scan length. At the same time, the encoder signal is obtained as a function of time. Note that if the paper feeding mechanism has high linearity accuracy, linearization of data may not be necessary. The data is obtained by the PIC 30 taking the data from the ADC 31. The data points are transmitted from the PIC 30 to the PC34 in real time. Alternatively, the data points may be stored in the memory of the PIC 30 and then transferred to the PC34 at the end of the scan. Hereinafter, the number of data points per detector channel N collected in each scan is defined as N. In addition, the value a is compared_k(i) Defined as the ith stored intensity value from photodetector k, where i is from 1 to N. An example of two raw data sets obtained from such a scan is shown in fig. 8A.

Step S2 locally expands and contracts a using numerical interpolation_k(i) So that the encoder transitions are equally spaced in time. This corrects for local variations in motor speed. This step is performed by a computer in the PC34And (6) executing the program.

Step S3 is an optional step. This step, if performed, numerically differentiates the data with respect to time. It may also be desirable to apply a weak smoothing function to the data. Differentiation can be used for highly structured surfaces because it attenuates uncorrelated effects from the signal relative to correlated (speckle) effects.

Step S4 is a step of averaging the recorded signals at N data points for each photodetector. For each photodetector, the average is subtracted from all data points, so that the data is distributed around 0 intensity. Reference is now made to fig. 8B, which shows an example of scanning a data set after linearization and subtraction of the calculated average.

Step S5 digitizes the analog photodetector data to calculate a digital signature representation of the scan. The digital signature is obtained by applying the following rules: a is_k(i) > 0 maps to a binary "1", and a_k(i) 0 maps to a binary "0". Defining the digital data set as d_k(i) Where i is from 1 to N. The signature of the article may advantageously contain other components than the digitized signature of the intensity data just described. These additional optional signature components are now described.

Step S6 is an optional step in which a smaller "thumbnail" digital signature is created. This is done by averaging the adjacent m reading groups, or preferably, by picking up every c-th data point, where c is the compression factor of the thumbnail. The latter is preferred because averaging may disproportionately amplify the noise. The same digitization rules used in step S5 apply to the reduced data set. Defining the digitization of a thumbnail as t_k(i) Wherein t is 1 to N/e, and c is a compression factor.

Step S7 is an optional step that applies when there are multiple detector channels. The additional component is a cross-correlation component calculated between intensity data obtained from different photodetectors. There is one possible cross-correlation coefficient for 2 channels and up to three cross-correlation coefficients for 3 channelsNumber, and 4 channels there are up to 6 cross correlation coefficients, etc. Cross-correlation coefficients are useful because they have been found to be good indicators of material type. For example, for a particular type of document, such as a specified type of passport or laser print paper, the cross-correlation coefficient always appears to be within a predictable range. Can be at a_k(i) And a_l(i) A standard cross-correlation is calculated between, where k ≠ l, and k, l varies across all photodetector channel numbers. The standard cross-correlation function Γ is defined as follows:

the use of cross-correlation coefficients in the verification process is described further below.

Step S8 is another optional step of calculating a simple intensity average representing the signal intensity distribution. This may be an overall average for each of the averages of the different detectors, or an average for each detector, such as a_k(i) Root mean square value of (d). If the detectors are arranged in pairs on either side of normal incidence, as in the reader described above, then the average for each pair of detectors may be used. It has been found that the intensity values are a good natural filter for the material type, as it is a simple representation of the overall reflectivity and roughness of the sample. For example, a non-standard root mean square value with the mean value (i.e., DC background) removed may be used as the intensity value.

The digital signature data obtained from the scanned article is then written into the database by adding the new record and the image file printed on the substrate and the associated literature data. The new database record will include the digital signature obtained in step S5 and, optionally, its smaller thumbnail version for each photodetector channel obtained in step S6, the cross-correlation coefficient obtained in step S7, and the average value obtained in step S8. In addition, the thumbnails may be stored on separate databases to optimize their own fast searches, and the remaining data (including the thumbnails) is stored on the main database. It should be noted that the same process is used when obtaining a digital signature that is subsequently used for verification purposes, as described below.

Fig. 10 is a flowchart showing a printing process in which paper being printed is scanned and a digital signature thereof is calculated and stored in a database. A user of PC 30 prepares a document using a word processor, drawing plug-in, or other type of application software for creating a document. A print command is issued whenever the document is ready. Then, an image file is created by the application software using an appropriate printer driver. The image file is then sent to a printer for printing. When paper on which an image is being printed is conveyed by a printer, a scanning head scans a portion of the paper. The scatter signals thus collected are converted into data points, as described above, and a digital signature is calculated according to the process described with reference to fig. 9. Then, a database record is created to store not only the digital signature, but also image files and related document data related to the creation of the document.

It should be noted that it is convenient to store the image file created by the printer driver, but this is not the only possibility. The image file may be another file type derived from the printer driver image file, or an image file in a preferred format of application software used to create the document or another format created by the application software. Another possibility would be an image file derived from a rescan of the document after printing. This can be done automatically, for example, in networked photocopiers and printing devices in the form of integrated document scanners with advanced paper feed (and re-feed) options. In this case, the image representation stored in the database will include any features on the substrate, as well as what is printed on the substrate. For example, if the paper is a paper with a title, the title will be included. This is advantageous in many cases. Various scenarios are possible. It is important to store some type of visual representation of what is printed.

The foregoing describes how documents are scanned at a source within a printing device each time they are generated, in order to obtain a digital signature unique to the paper or other substrate on which some representation has been printed, and the digital signature is stored in a database with the printed representations. The following describes how documents generated in this manner can later be validated as authentic, or tested to determine whether they were generated by an authorized source.

Fig. 11 is a schematic side view of a portable scanner or reader device 1 for scanning documents or other items for authentication purposes. It is apparent that the optical design is essentially the same as the scanning head of fig. 1A, which is mounted in a printer. For ease of comparison, the same reference numerals are used for the same components. The principle difference between the two designs is that the scanner of fig. 11 moves the scanner head and holds the article stationary, while the printer-based scanner described above moves the paper over the stationary scanner head.

The optical reader device 1 is used to measure a signature from an article (not shown) placed in the reading volume of the device. The reading volume is formed by a reading aperture 7, the reading aperture 7 being a slit in the housing 12. The housing 12 contains the primary optical components of the device. The slit has a main extent in the x-direction (see the insertion axis in the figure). The main optical components are a laser source 14 for forming a coherent laser beam 15 and a detector arrangement 16 consisting of a plurality of k photodetector elements, where k is 4 in this example, denoted 16a, 16b, 16c and 16 d. The laser beam 15 is focused by a cylindrical lens 18 to an elongated focal point extending in the y-direction (perpendicular to the plane of the figure) and located in the plane of the reading aperture. In this exemplary prototype reader, the elongated focal spot had a major axis dimension of about 2mm and a minor axis dimension of about 40 microns. These optical components are contained in the scan head assembly 20. Further details of the optical design are as described in particular in relation to fig. 1A and 1B and are therefore not repeated here.

A drive motor 22 is arranged in the housing 12 for providing linear movement of the optical assembly 20, as indicated by arrow 26, via suitable bearings 24 or other means. The drive motor 22 is thus used to linearly move the coherent light beam over the reading aperture 7 in the x-direction so that the light beam 15 is scanned in a direction transverse to the main axis of the elongate focus.

The acquisition is as described above in relation to the printer scanner, i.e. as shown in fig. 2, and is not repeated here.

Fig. 12 is a schematic block diagram of functional components of a reader device. The motor 22 is connected to a Programmable Interrupt Controller (PIC)30 via an electronic link 23. The detectors 16a.. d of the detector module 16 are connected by respective electrical connection lines 17a.. d to a digital-to-analog converter (ADC) which is part of the PIC 30. It will be appreciated that optical or wireless connections may also be used instead of or in combination with electrical connections. The PIC 30 is connected to a Personal Computer (PC)34 by a serial connection 32. The PC34 may be a desktop or laptop computer. As an alternative to a PC, other intelligent devices may be used, such as a Personal Digital Assistant (PDA) or a dedicated electronic unit. The PIC 30 and the PC34 together form a data acquisition and processing module 36 for determining a signature of an article from the set of data points collected by the detectors 16a. The PC34 accesses a database (dB)40 via an interface connection 38. The database 40 may reside in memory on the PC34 or stored on a drive thereof. In addition, the database 40 may be remote from the PC34 and accessed via wireless communication, such as using a mobile telephone service or a wireless Local Area Network (LAN), in conjunction with the internet. In addition, the database 40 may be stored locally on the PC34, but downloaded periodically from a remote source.

The database 40 contains a library of previously recorded signatures. The PC34 is programmed to access the database 40 in use and to perform a comparison to determine whether the database 40 contains a match with the signature of an item already located in the reading volume.

Fig. 13 is a perspective view of the reader device 1 showing the outer appearance thereof. The housing 12 and the slit-shaped reading aperture 7 are easily visible. The physical position aid 42 is also evident and provides for positioning an item of a given profile in a fixed position in relation to the reading aperture 7. In the example shown, the physical position aid 42 is in the form of a right angle stand in which the corners of the document or package can be positioned. This ensures that the same part of the article can be positioned in the reading aperture 7 whenever it is desired to scan the article. For items with well-defined corners, such as paper, passports, ID cards and packaging boxes, a simple corner bracket or equivalent is sufficient.

An alternative to a slotted aperture for the package would be to provide a suitable guide aperture, such as a rectangular cross-section aperture for receiving the base of a rectangular box, or a circular cross-section aperture for receiving the base of a tubular box (i.e. a cylindrical box).

FIG. 14 is a flow chart showing how the signature database is compared to verify the signature of an article obtained from a scan.

In a simple implementation, the database can simply be searched to find a match based on the entire signature data set. However, to speed up the verification process, it is preferable to use smaller thumbnails and a pre-screening based on the calculated average and the cross-correlation coefficients now described.

After scanning the article according to the above-described procedure, i.e., after performing the scanning steps S1 to S9 shown in fig. 9, the authentication procedure occurs.

The verification step V1 takes each thumbnail item and evaluates it against t_k(i + j), where j is a bit offset that is changed to compensate for a position error of the scanning area. The value of j is determined and then the thumbnail item that gives the largest number of matching bits is determined. This is a "hit" for further processing.

The verification step V2 is an optional pre-screening test performed prior to storing an all-digital signature for recording relative to the scanned digital signature analysis. In this pre-screening, the root mean square value obtained in the scanning step S8 is compared with the corresponding stored value in the hit database record. If the respective averages do not match within a predetermined range, a "hit" is rejected for further processing. The item is then rejected as unverified (i.e., the end is jumped to and a failure result is issued).

The verification step V3 is an additional optional pre-screening test performed before analyzing the complete digital signature. In this pre-screening, the cross-correlation coefficients obtained in step S7 are again compared with the corresponding stored values in the hit database records. If the respective cross-correlation coefficients do not match within a predetermined range, a "hit" is rejected for further processing. The item is then rejected as unverified (i.e., the end is jumped to and a failure result is issued).

The verification step V4 is the primary comparison between the scanned digital signature obtained in the scanning step S5 and the corresponding stored value in the hit database record. The whole stored digital signature d_k ^db(i) Into n blocks of q adjacent bits on k detector channels, i.e. each block has qk bits. A typical value for q is 4 and a typical value for k is 4, so that each block is 16 bits. Then, qk bits are compared with the stored digital signature d_k ^dbThe qk corresponding bits in (i + j) are matched. If the number of matching bits in a block is greater than or equal to some predetermined threshold Z_threshThe number of matching blocks is incremented. Z_threshWith a typical value of 13. This operation is repeated for all n blocks. This entire process is repeated for different offset values j to compensate for the position error of the scanning area until the maximum number of matching blocks is found. Defining M as the maximum number of matching blocks, the probability of a chance match is calculated by evaluating:

where s is the probability of a casual match between any two blocks (which, in turn, depends on Z)_threshIs selected), M is the number of matching blocks, and p (M) is the probability that M or more blocks match by chance. The value of s is determined by comparing blocks within a database of scans of different objects from similar materials, e.g., multiple scans of a paper document, etc. For q 4, k 4 and Z_threshA typical value for s is found to be 0.1 for the case of 13. If the qk bits are completely irrelevant, then for Z_threshProbability theory will yield s 0.01. The fact that higher values are found empirically is due to the correlation between k detector channels and the correlation between adjacent bits in the block due to the limited laser spot width. When comparing database entries for a sheet of paper, a typical scan of that sheet yields about 314 matching blocks out of a total of 510 blocks. For the above equation, setting M314, n 510, and s 0.1 yields 10^-177Chance match probability.

The verification step V4 issues the result of the verification process. The probability results obtained in the verification step V4 may be used in a success/failure test, where the benchmark is a predetermined probability threshold. In this case, the probability threshold may be set at one level by the system, or may be a variable parameter set at a level selected by the user. Additionally, the probability results may be output to the user as a confidence rating, either in the original form of the probability itself or in an improved form using relative terms (e.g., no match/bad match/good match/excellent match) or other categories.

It will be appreciated that many variations are possible. For example, instead of using the cross-correlation coefficients as the pre-filter components, they may be used as part of the primary signature along with the digitized intensity data. For example, the cross-correlation coefficients may be digitized and added to the digitized intensity data. The cross-correlation coefficients can also be digitized on themselves and used to generate bit strings, etc., and then thumbnails of the digitized intensity data can be searched in the same manner as described above to find hits.

FIG. 15 is a flowchart showing the overall process of how a document is scanned for verification purposes and the results provided to the user. First, a document is scanned using the scanning system of fig. 11 to 13. The process of FIG. 14 is then used to verify document authenticity. If there is no matching record in the database, a "no match" result is displayed to the user. If there is a match, it is displayed to the user in the manner now described.

FIG. 16 is a screen shot of a user interface displayed when the rescanned document is verified as authentic. In the primary right window, a visual representation of the documents stored in the database record with matching digital signatures is displayed. This is an electronic copy of the document associated with the matching digital signature. In this figure, the document is a letter formally offering a loan. Another example would be a photo page of a passport, but it will be appreciated that there are unlimited examples. On the left side of the screen there is a confidence indicator bar. This is a graphical representation of the possible results, as described with reference to fig. 14. The bar is labeled from left to right as a relative label for the quality of the match by "bad-normal-good-excellent". Some document data is also shown, i.e. some narrative text descriptions of documents are displayed in a large text window. For example, when the application software environment includes a document management system, this may be automatically generated at the source. The smaller text window displays document data identifying the printer that generated the document, the user ID of the user who generated it, and the date/time of generation. Database statistics are also shown, such as the record number shown in the lower left corner of the screen.

It is thus clear that when a database match is found, the user is provided with relevant information in an intuitive and accessible way to allow the user to apply his or her own general knowledge for additional informal layer authentication. It is clear that the document image should look like the document provided to the verifier and that other factors, such as trustworthiness and bibliographic data related to the document itself, will be of interest. The examiner will be able to apply their experience to make valuable judgments about whether these various pieces of information agree on themselves.

Another implementation of the present invention will now be described.

Fig. 17 shows an ID card 50 having a barcode. The ID card may also have a separate security element 54, such as a photograph, hologram, or contain some biometric information specific to the individual. The barcode is shown as part of the scan area 56. Illustrated with a dashed line because it is not distinctive on an ID card. The scan area is subdivided into a lower region 52 containing the bar code and a blank upper region 58. The ID card 50 is designed to be scanned by a reader device of the type shown in fig. 6B, in which one set of directional detectors is used to scan the barcode region 52 and two other sets are used to scan the upper region 58. In this embodiment, the barcode code is a signature obtained by scanning the blank upper area using the method of the present invention.

Put another way, according to the method of the present invention, a bar code is initially applied at the time of manufacture of the ID card by scanning a blank upper region of the card, and then printed on the lower region 52. The ID card is thus marked by its inherent structure, i.e. signature properties of the surface structure in the upper region 58.

It will be appreciated that this basic method may be used to mark a large number of articles, such as any printable article, including paper or cardboard articles or plastic articles, by a label encoding a signature of the article itself derived from its inherent physical properties.

Given the common nature of barcodes or other tags that follow a publicly known encoding protocol, it is recommended to make sure that the asymmetric encryption algorithm used to create the barcode has been used, i.e., to transform the signature using a one-way function, such as according to the well-known RSA algorithm. A preferred implementation is a label to represent a public key in a public/private key encryption system. If the system is used by a number of different users, it is recommended that each client has its own private key, so that the disclosure of the private key will only affect one client. The tag thus encodes the public key, and the private key is securely located by authorized personnel.

In one embodiment, a printing apparatus with a dual paper feeder is used, allowing paper to pass through it twice. This may be done once on each side for duplex printing, or twice on the same side for printing on the same side. A first pass is used to obtain a unique digital signature from the sheet using a scanning head integrated in the printing device. The second pass then immediately prints a barcode or other encoded indicia containing an encrypted version of the digital signature on the paper. This provides the possibility of "database-less" verification of the document, although it is clear that the stored image of the document cannot be verified without reference to the database. Other information may also be added to the barcode. A specific example that may be used is printing a check. The value of the check and, optionally, a hash of the drawer's name may be included in the barcode.

In another embodiment, paper or other printable items are first scanned to allow the digital signature to be determined before any printing occurs. The printing of the image and the barcode-encoded digital signature may occur in one printing action.

It will be further understood that barcodes or other labels can also be used to encode other information pertaining to or unrelated to the digital signature.

Another predictable advantage of the tagging approach is that the novice user, without expert knowledge, will not know the verification performed. It is natural for the user to assume that the reader device is a simple bar code scanner and that it is a bar code that is scanned.

A tagging scheme can be used to allow items to be verified purely on the basis of tags without accessing a database. In principle, this is a similar approach to the failed banknotes reported in prior art [1 ].

However, it is also contemplated that the tagging scheme may be used in conjunction with a database validation scheme. For example, the barcode may encode a thumbnail version of the digital signature and may be used to allow for rapid pre-screening before screening against a database. This can in fact be a very important approach, as potentially in some database applications the number of records will become huge (e.g., billions), and search strategies will become critical. Inherently high speed search techniques, such as using bit strings, will become important.

As an alternative to a barcode encoding the thumbnail, the barcode (or other tag) may encode a record locator, i.e., an index or bookmark, which can be used to quickly find the correct signature in the database for further comparison.

Another variation is that the barcode (or other tag) encodes a thumbnail signature that can be used to obtain a match with reasonable but not high confidence if the database is not available (e.g., temporarily offline, or scanned at a very remote location without internet access). Then, if the database is available, the same thumbnail can be used for fast record location within the main database, allowing higher confidence verification to be performed.

Fig. 18 is a schematic plan view of an ID card 50, a so-called smart card, which contains a data carrying chip 55. The data carried by the chip 55 comprises signature coded data encoding a digital signature obtained from the inherently measured surface property of the ID card 50 obtained from the scan field 56, the scan field 56 being featureless in this example as shown by the dotted line but could be decorated in any desired manner or contain, for example, a photograph.

Fig. 19 is a schematic plan view of the warranty document 50. The scanning area 56 includes two barcode labels 52a, 52b arranged one above the other that encode a digital signature derived from the inherently measured surface characteristics, similar to the ID card example of fig. 17. The barcodes 52a, 52b are arranged above and below a digital signature scan area 58 for a personal signature 59, as shown schematically. At least the area 58 is preferably covered with a transparent adhesive cover for tamper resistance.

Many other commercial examples will be envisaged, the above figures 17 to 19 being given by way of example only.

From the above detailed description it will be understood how an article made of printable material, such as paper or cardboard or plastic, is identified by exposing the material to coherent radiation, collecting a set of data points measuring the scattering of the coherent radiation from the intrinsic structure of the material, and determining a signature of the article from the set of data points.

It will also be appreciated that the size of the scanning zone or location on the printable surface of the item is virtually arbitrary. If desired, the scan may be a linear scan that is rasterized to cover a larger two-dimensional area, for example.

Furthermore, it will be understood how this will be applied in order to identify a product by its packaging, document or item of clothing by exposing the item to coherent radiation, collecting a set of data points measuring the scattering of the coherent radiation from the intrinsic structure of the material, and determining the signature of the item from the set of data points.

From the above description of numerical processing, it will be appreciated that a reduction in beam localization (e.g. beam cross-section enlargement in the reading volume due to non-ideal focusing of the coherent beam) will not be catastrophic to the system, but will only reduce its performance by increasing the chance match probability. Thus, the device is robust to device variations, providing a steady step-down in performance, rather than a sudden unstable failure. In either case, it is simple to perform a self-test of the reader, whereby any device problem is picked up by performing an autocorrelation on the collected data in order to determine the characteristic minimum feature size in the response data.

Another security measure that can be applied to paper or cardboard is, for example, the sticking of a transparent seal (e.g. tape) on the scanning area. The adhesive is chosen to be strong enough so that removal of it will destroy the underlying surface structure that must be protected in order to perform the verification scan. The same method can be applied to the deposition of a transparent polymer or plastic film on a card or on a package with similar material.

As mentioned above, the reader may be embedded in a device specifically designed to implement the present invention. In other cases, the reader is designed by adding suitable auxiliary components to devices that are in principle designed with another functionality, such as copiers, document scanners, document management systems, POS devices, ATMs, ticket boarding card readers or other devices.

The skilled person will be able to envisage many other variations of the invention than those specifically mentioned above.

It will be appreciated that although specific embodiments of the invention have been described, many modifications/additions and/or substitutions may be made within the spirit and scope of the invention.

Reference book eye

[1]PCT/GB03/03917-Cowburn

[2]GB 2 221 870 A-Ezra，Hare & Pugsley

[3]US 6,584,214-Pappu，Gershenfeld & Smith

[4]Kravolec“Plastic tag makes foolproof ID”TechnologyResearch News，2 October 2002

[5]R Anderson“Security Engineering：a guide to buildingdependable distributed systems”Wiley 2001，pages 251-252 ISBN0-471-38922-6

[6]US 5,521,984

[7]US 5,325,167

Claims (9)

1. A printing apparatus comprising:

a feed mechanism for conveying the article past the print head;

a scanning head comprising a coherent source and a detector arrangement, wherein the coherent source is arranged to sequentially direct light onto each of a plurality of surface regions of an article conveyed by a feed mechanism, and the detector arrangement is arranged to collect a set comprising sets of data points from signals obtained when scanning light over the article, wherein different sets of data points relate to surface structure induced scattering from different respective surface regions of the article; and

the print head is to print an image on an article and encode a digitally signed label pattern of the article determined by the set of data points according to a machine readable encoding protocol.

2. The printing apparatus of claim 1, wherein the feed mechanism is to convey the article past the printhead at least twice so that the article can be printed multiple times.

3. A printing device as claimed in claim 1 or 2, wherein the article is a paper or cardboard document.

4. The printing device of claim 1, wherein the digital signature is encoded into the label using an asymmetric encryption algorithm.

5. The printing device of claim 4, wherein the label represents a public key in a public/private key encryption system.

6. An apparatus for creating an authenticatable article, comprising:

a printer driver to create an instruction for the printing apparatus to print an image;

a data acquisition interface for receiving a set comprising sets of data points from signals obtained by sequentially scanning light over each of a plurality of surface areas of the article during printing, wherein different sets of data points relate to scattering caused by surface structures from different respective surface areas of the article; and

a processor for determining a digital signature of the item from the set of data point groups and for determining a printable label pattern encoding the digital signature according to a machine-readable encoding protocol;

wherein the printer driver is further operable to create instructions for the printing device to print a label design on the article.

7. The apparatus of claim 6, wherein the digital signature is encoded for the printable label pattern using an asymmetric encryption algorithm.

8. The apparatus of claim 7, wherein the printable label pattern represents a public key in a public/private key encryption system.

9. The apparatus of any one of claims 6-8, wherein the article is a paper or cardboard document.