WO2017100952A1

WO2017100952A1 - Method and device for verifying the authenticity of a security document

Info

Publication number: WO2017100952A1
Application number: PCT/CH2015/000187
Authority: WO
Inventors: Martin Eichenberger; Sylvain Chosson
Original assignee: Orell Füssli Sicherheitsdruck Ag
Priority date: 2015-12-17
Filing date: 2015-12-17
Publication date: 2017-06-22

Abstract

A security document (1) is provided with fine surface structures (10), which can e.g. be generated by intaglio print, embossing or lamination. In order to verify the authenticity of the document, the surface structures (10) are pressed against a spatially resolving force sensor (28). The pattern scanned by the force sensor (28) can then be analyzed, e.g. by comparing it to a number of reference patterns.

Description

Method and device for verifying the authenticity of a security document

Technical Field

The invention relates to a method and a device for verifying the authenticity of a security document .

Background Art

A variety of methods is known for the machine-assisted verification of the authenticity of a security document, such as a banknote, a cheque, a stock certificate or an identification document. These methods include optical verification techniques , techniques for reading invisible features (such as infrared markings or markings based on UV-excitable fluorescent dyes) , or techniques for detecting magnetic features.

However, there is always need for new tech^¬ niques of this type in order to make counterfeiting harder, e.g. because the security of a document increases when it can be verified by several different techniques .

Disclosure of the Invention

Hence , it is a general object of the invention to provide an alternative method and device for verifying the authenticity of a security document .

This object is achieved by the method of claim 1.

Accordingly, the method for verifying the au^¬ thenticity of a security document by means of an authen- tication device comprises the following steps:

- Pressing at least a part of the security document having characteristic surface structures against a spatially resolving force sensor of said authentication device, or against a point force sensor of said authentication device that is moving in respect to said surface structures. By doing so, the surface structures will gen^¬ erate a spatial or temporal force pattern acting on the force sensor, which can be scanned by the force sensor.

- Generating a scan of said surface structures by means of said force sensor: Since the force pattern acting on the force sensor is basically due to the surface structures, the scan recorded by the force sensor is a representation of the surface structures, i.e. the surface structures are recognizable within the scan.

- Deriving the authenticity of said security document from said scan: This step typically involves checking at least one characteristic feature of the scan. A number of methods to be used in this check are given belo .

For example, the "step of deriving the authenticity of said security document from said scan" can e.g. comprise one or more of the following steps:

- Comparing said scan to at least one reference pattern stored in said authentication device: This comparison can e.g. be carried out using known image comparison techniques.

- Checking said scan for a predefined feature: This technique does not necessarily require reference patterns stored in the authentication device, but relies on testing if the scan has a certain property. Ex^¬ amples of such properties are described below.

The surface structures that are scanned can be of a variety of techniques, in particular:

- The surface structures can be formed, at least in part, by intaglio print, i.e. by inks applied by means of intaglio printing . As known to the skilled person, intaglio printing can be used to form detectable surface structures . - The surface structures can be formed, at least in part, by an embossed mark of the security document .

- The surface structures can be formed, at least in part, by a structured layer applied, directly or indirectly, to a substrate of the security document. Such a structured layer can e.g. be a structured transfer foil with a thickness sufficient to generate surface structures that can be detected by the force sensor.

The authentication device according to the invention comprises

- A spatially resolving force sensor: This is the sensor to be used for scanning the surface of the security document.

- A control unit: This control unit is adapted and structured to generate a scan of the surface structures of a security document pressed against said force sensor and to derive the authenticity of the security document from said scan.

The authentication device is advantageously a phone or a tablet computer. However, it can also be a dedicated device adapted to a single purpose only.

The force sensor is advantageously integrated into a touch-sensitive display of the authentication device or into a fingerprint sensor of the authentication device .

Brief Description of the Drawings

The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof . This description makes refer^¬ ence to the annexed drawings, wherein:

Fig. 1 shows a banknote as an example of a security document, Fig. 2 shows a sectional view along line II- II of Fig. 1,

Fig. 3 shows an authentication device,

Fig. 4 is a simplified block diagram of the authentication device,

Fig. 5 shows the step of pressing the security document against the force sensor,

Fig. 6 shows a sectional view of a second em bodiment of the surface structures,

Fig. 7 shows a sectional view of a third em^¬ bodiment of the surface structures,

Fig. 8 illustrates a method for scanning sur face structures by means of a point force sensor,

Fig. 9 shows the force recorded by the point force sensor versus time, and

Fig. 10 illustrates yet another scanning method.

Modes for Carrying Out the Invention

D finitions :

The term "security document" refers to any document that may require a verification of authenticity, i.e. the term is to be understood broadly. However, the invention is particularly suited for verifying the authenticity of banknotes, cheques and identification documents .

The term "spatially resolving force sensor" refers to a sensor that has a scanning area and that is able to measure forces acting on said scanning area in spatially resolved manner. In other words, the sensor is able to record a spatially resolved one- or two-dimensional image of the forces acting on it.

The term "point force sensor" refers to a sensor that measures the force acting on a small sensing a rea thereof . In this context, a "small" sensing area is an area much smaller than the total lateral extension of the surface structures and advantageously not larger than the lateral extension of individual structure elements of the surface structures.

An "embossed mark" is a mark formed by a deformation of the security document by means of embossing or debossing, in particular by means of a pair of dies between which the substrate of the security document or of a foil to be applied to the security document has been compressed, e.g. in the course of the intaglio printing process or in a separate step. The embossed mark can be formed in the substrate of the security document or in a foil applied to the substrate of the security document.

Security document:

Fig. 1 shows a security document 1 in the form of a banknote having a flexible substrate 2, which can e.g. be of paper, cotton, polymer or a combination thereof. Substrate 1 can carry a variety of security fea^¬ tures, such as intaglio-printed motifs 3, 4, 5, an embossed mark 6 embossed into substrate 2, and a foil element 7 laminated to substrate 1. Foil element 7 carries in turn a mark 8, which can e.g. again be embossed or in^¬ taglio printed in foil element 7, or which can e.g. be a metallic or non-metallic structure 8 applied to foil element 7.

Security document 1 can also be equipped with a perforation extending through substrate 2 . Such perforations are e.g. known from US 2006/006236 and can e.g. be formed by laser pulses.

At least part of these security features give rise to a characteristic relief on the surface of substrate 1.

This characteristic relief advantageously comprises a plurality of structures 10 arranged on a first side 11 of substrate 2 , such as shown in Fig. 2 for the example of motif 4. In order to be easily detectable by means of the technology described below, the surface structures 10 should have at least one, advantageously several or all, of the following features:

- The height H of the structures 10 (i.e. the extension perpendicular to substrate 1) is advantageously between 10 μπι and 100 μτη, in particular between 20 μπι and 40 μπι. Structures within these height ranges can be well detected by the techniques described below without adding to much thickness to the security document.

- The total lateral extension D of the structures 10 (i.e. the total extension of the whole assembly of structures in at least one direction, advantageously in at least two perpendicular directions, parallel to substrate 1) is advantageously at least 5 mm, in particu^¬ lar at least 10 mm. Again, an arrangement of structures of such extension can be well detected by the techniques described below.

- At least a plurality of the structures 10 should have distances d of neighboring edges in a range smaller than 2000 μιη, in particular smaller than 500 μτα, which is much smaller than a typical fingertip and can therefore be resolved as a structure when a finger is used for pressing the document against the force sensor as described below. A minimum lateral distance is advantageously at least 1 μιη for easy detection.

- The edges of the structures 10 are advantageously "sharp" in order to obtain a good signal contrast in the force sensor described below. Hence, the width w of at least some of the edges of the surface structures 10, as seen along a direction of view perpendicular to substrate 1, is advantageously less than the height H of the surface structures. For illustration purposes, such edges 13 are shown for one of the structures 10 of Fig.

2.

As shown in Fig. 2, the security document advantageously carries a target marker 15 on substrate 1 at a second surface 14 of substrate 2. The target marker 15 is located opposite the structures 10, i.e. at substantially the same location as the structures 10 but merely on the other side of substrate 2. Target marker 15 is visually perceptible to the human observer and allows him/her to identify the position of the structures 10 when viewing document 1 from second side 14.

Target marker 15 can e.g. a printed marker.

In the embodiment of Fig. 2, the structures 10 are formed by the intaglio printed motif 4. However, the structures 10 can also be formed by one of the other intaglio printed motifs 3 or by the embossed mark 6.

The structures 10 can also be formed by a metallic or non-metallic structured layer applied to substrate 1 or to foil element 1, such as structure 8 on foil element 7.

The structures 10 can also be formed by the perforations 9. These perforations advantageously extend through all of security document 1, i.e. they are formed by "through-holes", but they may also extend only through part of the security document, i.e. they are formed by "blind holes". The perforations can e.g. extend through substrate 2, through foil element 7, or through both these elements.

The surface structures can also be created by a combination of the above techniques, e.g. by intaglio printing onto laminated surface structures.

Authentication device:

Fig. 3 shows an embodiment of an authentication device 20. It typically comprises a housing 21 holing a variety of components,, such as a display 22 and/or one or more user-operatable input elements 23. Display 22 may be a touch-sensitive display.

Advantageously - and as already mentioned - authentication device 20 is a mobile phone and/or a tablet computer . Some of the components of authentication device 20 are depicted in the block diagram of Fig. 4. It comprises a control unit 24, which is e.g. a microprocessor equipped with software for controlling the operation of the device. Control unit 24 is connected to a memory 25 holding not only said software but also various data, some of which is described in more detail below.

If authentication device 20 is a mobile phone, it comprises radio transceivers 26 as known to the skilled person for data and/or voice communication.

As mentioned, authentication device 20 further comprises a display 22, in particular a touch-sensi^¬ tive display, and/or one or more user-operatable input elements 23.

Further, authentication device 20 is equipped with a spatially resolving force sensor 28.

Force sensor 28 can use any known force sensor design that has a resolution sufficient to resolve the structures 10 when these structures are pressed against it, e.g. by means of a finger 30, as shown in Fig. 5.

Force sensor 28 can e.g. comprise a sensing array such as described in WO 2015/066599, where a large number of piezo-electric sensing elements are provided for a spatially resolved detection of a force pattern. Alternatively, techniques as described in WO2014037016 can be used.

Some of these force sensor technologies allow the manufacturing of transparent sensors, e.g. WO

2015/066599 or WO2014037016. Hence, display 22 of the de^¬ vice can e.g. be a touch-sensitive display using such a force sensor.

Alternatively, or in addition thereto, the force sensor can also be integrated in a fingerprint sen^¬ sor of the device, which may be separate from display 22, e.g. integrated in input element 23. In conventional devices, such a fingerprint sensor is typically used for unlocking the device. In the present application, force sensor 28 can be used for fingerprint detection as well as document verification because both tasks are based on scanning surface structures of comparable dimensions.

Control unit 24 of authentication device 20 is adapted and structured to generate a scan of the surface structures 10 of the security document pressed against force sensor 28. Such a scan can e.g. be triggered automatically or started as soon as the device detects the presence of potentially qualifying surface structures by means of force sensor 28.

Once the structures have been scanned, control unit 24 runs the authentication method as described below and displays a result thereof on display 22.

These steps are typically carried out by software stored e.g. in memory 25 and executed by control unit 24.

Authentication method:

In order to authenticate a security document, the user presses the document with the structures 10 against force sensor 28, advantageously with a finger 30 or a palm, as illustrated in Fig. 5. Target mark 15 can be used for properly placing the structures 10 over force sensor 28 if force sensor 28 is small, and for applying the pressure at the correct location.

Authentication device 20 will then scan the force pattern and process it further.

In one embodiment, the scanned pattern can be compared to a number of reference patterns stored in memory 25 of the device using conventional image recognition techniques that compensate for rotation and offset between the scanned pattern and the stored reference pat^¬ terns .

For example, a suitable algorithm can comprise the following steps for comparing the scanned pattern with a given reference pattern : 1. Calculate the two-dimensional correlation between the scanned pattern and the reference pattern.

2. Numerically rotate the scanned pattern (or the reference pattern) by a small angle then repeat steps one and 2 until the numerical rotation reaches 360°.

A suitable algorithm can also use other image processing algorithms for determining the similarity of two images. For example, it can be based on feature matching or template matching techniques as e.g. implemented by the opencv software package (see

http://opencv.org) .

A high correlation peak in one of the steps 1 is then indicative of a match between the reference pattern and the scanned pattern.

In another embodiment, the scan can be checked for certain features without using stored reference patterns. For example, control unit 24 can e.g. calculate the two-dimensional Fourier transform of the scanned pattern and check this transform for the presence and/or absence of certain harmonics. For example, a regular stripe pattern as shown under reference number 8 in Fig. 1 will give rise to a very specific spectral distribution of the Fourier components with marked peaks representing the line repetition frequency and (depending on the lines' contours) the harmonics thereof.

The above comparison of the scan to reference patterns can also be combined with the above checking for certain features without using stored reference patterns, thereby providing a redundant check with increased relia^¬ bility.

Further embodiments:

Fig. 6 shows a further embodiment of a security document 1. This document again comprises a substrate 1 with first structures ( lOa-1 , 10a2) applied to its first side 11. In addition, it comprises second structures (lOb-1, 10b-2 ) applied to its second side 14 opposite first side 11. The first and second structures overlap at least partially, in particular only partially. In their overlapping regions, they form sub-regions A, B, C, D and E where the overall document 1 has different thickness. In the embodiment as shown, the first and second structures form the following sub-regions:

- Sub-region B, D: No structure is present on any of the sides 11, 14 of document 1.

- Sub-region C: A structure is present on first side 11, but not on second side 14 of document 1.

- Sub-region A: A structure is present on second side 14, but not on first side 11, of document 1.

- Sub-region E: Structures are present on first and second side 11, 14 of document 1.

When pushing this type of document with a soft object against a force sensor by means of a resilient object, such as a finger, the force at the location of sub-region E is highest, while the force at sub-regions A and C are smaller, with the force at sub-regions B and D being the smallest.

If the structures on the two sides 11, 14 are of different thickness, the forces in sub-regions A and C will differ accordingly.

Hence, scanning the structures as described above by means of a force sensor allows checking the two structures and their mutual registration on opposite sides of the document, which allows an even more reliable verification of authenticity.

Fig. 7 shows a further embodiment where the surface structures 10 contain regions of at least three different heights (one of which may have zero height) . Advantageously, each such region has a lateral extension of at least 100 μπι for being detected individually, and/or the height differences between the regions are at least 10 μπι. A surface structure as shown in Fig. 7 can e.g. be formed by a single one or a combination of more than one of the following methods:

- varying the depth of the grooves of an intaglio printing plate,

- printing several voluminous ink layers (e.g. of thermochromic ink) on top of each other, and/or

- ink-jet printing using any suitable ink (including varnish) while controlling the amount of ink applied to each location,

- applying a single, structured voluminous ink layer (e.g. of thermochromic ink) over a substrate that already has surface structures, which has e.g. been formed by embossing or by perforating the substrate.

The technique of Fig. 7 can be applied to any of the surface structures shown herein, e.g. to the two- sided surface structures of Fig. 6 as well as to the onesided surface structure of Fig. 2.

Figs. 8 and 9 disclose a second way of scanning the structures.

While, in the embodiments above, the sensor was assumed to be a one-dimensional or two-dimensional force sensor, the sensor may also be a point force sensor structured to measure a force at one location, in particular a pen 30 with a force-sensing tip 31 as shown in Fig. 8.

In this embodiment, the user moves the force sensor 30, 31 over the surface structures 10 while contacting the same, as indicated by arrow 32, in substan^¬ tially linear movement with steady velocity, while the force sensor carries out a time-resolved measurement, giving rise to recorded force versus time data as shown in Fig. 9.

The recorded data can then be analyzed in order to check for a characteristic property of the structure. Processing the data can e.g. comprise the steps of - Timescale the signal trait to a standard length, thereby making the result independent on the scanning velocity.

- Calculate the derivative of the measured force versus time and process the result by means of high-pass filtering, thereby getting rid of any offset and slow-varying changes of force.

- Detect the peaks in the resulting data.

These peaks correspond to the locations of the edges of the surface structure.

- Compare the resulting edge locations to locations expected to be caused by the surface structures 10.

Various other algorithms are conceivable and are e.g. known from the art of ID-barcode scanning.

While the embodiment of Figs. 8 and 9 is best suited for scanning ID-barcode-like structures, i.e.

structures that require scanning only along one direction, Fig. 10 illustrates a method using a point force sensor 30, 31 that is adapted to also scan two-dimensional structures. In this method, the device for carrying out the present method contains, in addition to the point force sensor 30, 31, a position sensor for measuring the position of the force sensor 30, 31, advantageously in at least two dimensions. In that case, the user can place the document on a surface and start rubbing the surface structures 10 with force sensor 30, 31, e.g. using arbitrary motions, as indicated by the arrow in Fig. 10. By recording the force measured by force sensor 30, 31 together with its position, the authentication device is able to assemble a 2D force field image, which then can be analyzed e.g. using the image analysis methods described above.

The device can be adapted to show the scanned and not yet scanned parts of the structure on a display, thereby guiding the user to scan yet non-scanned parts of the pattern. In a specific embodiment, the device can e.g. comprise a tablet 32 having a flat surface (which can e.g. a touchscreen of the device) with integrated position sensors 33, e.g. capacitive position sensors able to detect the position of the force sensor 30, 31. Suitable techniques for such devices are known from tablets and smartphones and are e.g. described in US 2014/0028634.

When using such a device, the security document can be placed on the tablet 32 containing the position sensors 33, whereupon the point force sensor 30, 31 is moved along a random path over the structures while being pressed towards the tablet.

Information retrieval:

In a particularly advantageous embodiment, the structures can differ between documents, i.e. they can contain different information depending on the document they are applied to. The information can even be unique for each document.

For example, if document 1 is a banknote, the structures 10 can encode its serial number and/or its de^¬ nomination. If document 1 is a passport, the structures 10 can encode its holder's name and/or the country of origi .

For verification, the encoded information can then e.g. be compared to individualized alphanumeric or other human-readable information applied to the document, such as a serial number.

Individualized structures 10 can e.g. be generated using ink jet printing or printing with thermo- chromic inks, in particular if the structures are to encode information unique for each document.

Suitable encoding techniques are e.g. ID-bar- codes or QR codes.

Higher information densities can be achieved when using structures as shown in the embodiment of Fig. 7. Notes :

Force sensor 28 can be a one-dimensional or a two-dimensional force sensor. A two-dimensional force sensor comprises a two-dimensional matrix of sensing elements that allows a direct scan the two-dimensional shape of the structures 10 in the plane of substrate 2. A, one- dimensional force sensor comprises a one-dimensional array of sensors only. If a one-dimensional force sensor is used but a two-dimensional scan is required, the security document can be displaced in a direction perpendicular to the sensor array while carrying out repetitive measurements in order to scan the structures 10 in two dimensions. As mentioned above, the force sensor can also be a point force sensor 30, 31 that is moved relative to the structures to be scanned.

While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and prac^¬ ticed within the scope of the following claims.

Claims

1. A method for verifying the authenticity of a security document (1) by means of an authentication device (20) comprising the steps of

pressing at least a part of the security document (1) having characteristic surface structures (10) against a spatially resolving force sensor (28) of said authentication device (20) or against a point force sensor (30, 31) of said authentication device (20) that is moving in respect to said surface structures (10),

generating a scan of said surface structures (10) by means of said force sensor (28), and

deriving the authenticity of said security document (1) from said scan.

2. The method of claim 1 wherein said step of deriving the authenticity of said security document (1) from said scan comprises a comparison of said scan to at least one reference pattern stored in said authentication device (20) .

3. The method of any of the preceding claims wherein said step of deriving the authenticity of said security document (1) from said scan comprises checking said scan for a predefined feature.

4. The method of any of the preceding claims wherein said surface structures (10) are formed, at least in part, by intaglio print (3, 4, 5).

5. The method of any of the preceding claims wherein said surface structures (10) are formed, at least in part, by an embossed mark (6) of the security document (1) .

6. The method of any of the preceding claims wherein said surface structures (10) are formed, at least in part, by a structured layer (8) applied to a substrate (1) of the security document (1) .

7. The method of any of the preceding claims wherein said surface structures (10) are formed, at least in part, by perforations (9) extending through at least part of the security document (1) .

8. The method of any of the preceding claims wherein said authentication device (20) is a phone or a tablet computer.

9. The method of any of the preceding claims wherein said force sensor (28) is integrated into a fingerprint sensor (23) of said authentication device (20).

10. The method of any of the preceding claims wherein said force sensor (28) is integrated into a touch-sensitive display (22) of said authentication device (20) .

11. The method of any of the preceding claims wherein :

a height (H) of the structures (10) is between 10 μιη and 100 μηα, in particular between 20 μτ and

a total lateral extension (D) of the structures (10) is at least 5 mm, in particular at least 10 mm, and/or

at least a plurality of the structures (10) has lateral distances (d) between neighboring edges of less than 2000 μπι, in particular of less than 500 μπι, and/or of at least 1 μπι and/or

wherein a width (w) of a plurality of edges (13) of said surface structures (10) is less than a height (H) of said surface structures (10).

12. The method of any of the preceding claims wherein said surface structures (10) are arranged at least on a first side (11) of a substrate (2) of said security document (1) and wherein said security document

(1) comprises, on a second side (14 ) of said substrate

(2) and opposite said surface structures (10), a visually perceptible target mark (15) identifying a location of said structures (10).

13. The method of any of the preceding claims wherein said security document (1) comprises first surface structures (lOa-1, 10a-2) on a first side (11) of a substrate (2) and a second surface structures (lOb-1, 10b-2) on a second side (14) of said substrate (1), wherein said first and second surface structures overlap at least partially, in particular only partially.

14. The method of claim 13 wherein said first and second surface structures (10) form the following sub-regions :

- a sub-region where no surface structure is present on any of said first and second sides,

- a sub-region where a surface structure (lOa-1, 10a-2) is present on said first side (11) but no surface structure is present on said second side (14) ,

- a sub-region where a surface structures (lOb-1, 10b-2) is present on said second side (14) but no surface structure is present on said first side (11) , and

- a sub-region where said a surface structure (lOa-1, 10a-2) is present on said first side (11) and a surface structure (lOb-1, 10b-2) is present on said second si de (14) .

15. The method of any of the preceding claims wherein said surface structures (10) comprise at least three regions of different heights,

and in particular wherein each region has a lateral extension of at least 100 μτα, and/or height dif^¬ ferences between the regions are at least 10 urn.

16. The method of any of the preceding claims, wherein said force sensor is a point force sensor (30, 31) and wherein said device further comprises a position sensor for measuring a position of said point force sensor (30, 31) , in particular in at least two dimensions, and wherein said point force sensor ( 30 , 31 ) is moved over said structure while recording the force measured by said point force sensor (30, 31) as well as the position of said point force sensor (30, 31) for recording said scan.

17. The method of claim 16, wherein said de^¬ vice comprises a tablet (32) having a flat surface comprising position sensors (33) for said point force sensor (30, 31), and wherein said method comprises the step of placing the document (1) against the tablet (32) and moving the point force sensor (30, 31) over the surface structures while pressing it towards the tablet (32).

18. The method of any of the preceding claims, wherein said surface structures differ between documents and encode information depending on said document (1), and wherein said method comprises the step of retrieving, from said scan, said information.

19. An authentication device for verifying the authenticity of a security document (1) comprising a spatially resolving force sensor (28) or a point force sensor (30, 31) ,

a control unit (24) adapted and structured to

- generate a scan of surface structures (10) of a security document (1) pressed against said force sensor (28) and

- derive the authenticity of said security document (1) from said scan.

20. The authentication device of claim 19 wherein said authentication device is a phone or a tablet computer .

21. The authentication device of any of the claims 19 or 20 wherein said force sensor (28) is inte^¬ grated into a fingerprint sensor (23) of said authentication device.

22. The authentication device of any of the claims 19 or 20 wherein said force sensor (28) is integrated into a touch-sensitive display ( 22 ) of said au^¬ thentication device.