Abstract
A method for verifying the authenticity of a security document by means of a camera-equipped cellphone comprises steps of acquiring a transmission mode image and a reflection mode image of the security document. Transmitted light through a plurality of perforations in a substrate of the security document is evaluated by means of the cellphone. Then, a relative positioning of the perforations with respect to a printed security features is determined, and the security document is considered authentic if the determined positions and the acquired images substantially correspond to pre-stored templates for the security document. The perforations are structured such that they are not visible to the naked eye of a human observer which makes it harder to counterfeit the security document.
Claims
1. A method for verifying an authenticity of a security document, wherein said security document comprises a substrate, at least one perforation pattern in said substrate, and a security feature on said substrate, wherein said perforation pattern comprises a plurality of perforations of at least a part of said substrate, wherein to the naked eye of a human observer at least one of said perforations is not visible in a reflection mode, and wherein the method comprises steps of acquiring a transmission mode image of at least a part of said perforation pattern of said security document by means of a verification device, acquiring a reflection mode image of at least a part of said perforation pattern of said security document by means of said verification device, acquiring a reflection mode image and/or a transmission mode image of said security feature of said security document by means of said verification device, determining a relative positioning of at least one of said perforations with respect to said security feature, and verifying by means of said verification device said authenticity of said security document using said transmission mode image of at least said part of said perforation pattern, said reflection mode image of at least said part of said perforation pattern, said reflection mode image and/or said transmission mode image of said security feature, and said determined relative positioning.
2. The method of claim 1, wherein said verification device is selected from a group consisting of a camera-equipped cellular phone, a camera-equipped tablet computer, a digital camera, a camera-equipped laptop computer, a bank note sorter, and a bank note acceptor.
3. The method of claim 1, wherein at least one of said perforations of said substrate has a lateral dimension less than 200 microns in at least one direction parallel to a surface of said substrate.
4. The method of claim 1, wherein said perforations have different shapes and/or different lateral dimensions parallel to a surface of said substrate and/or different axial dimensions perpendicular to a surface of said substrate.
5. The method of claim 1, wherein all perforations have substantially the same shapes and the same lateral dimensions parallel to a surface of said substrate and the same axial dimensions perpendicular to a surface of said substrate.
6. The method of claim 1, wherein the security document comprises at least a first perforation pattern and a second perforation pattern, each perforation pattern comprising a plurality of perforations of said substrate, wherein said second perforation pattern is translated and/or rotated and/or mirrored and/or scaled with respect to said first perforation pattern.
7. The method of claim 1, wherein a first lateral dimension along a first axis parallel to a surface of said substrate of at least one of said perforations is different from a second lateral dimension along a second axis parallel to said surface of said substrate of said at least one of said perforations, and wherein said step of acquiring said transmission mode image is carried out at a non-zero tilt angle between an optical axis of said verification device and a third axis perpendicular to said surface of said substrate.
8. The method of claim 7, wherein said tilt angle is greater than 10 degrees.
9. The method of claim 7, wherein said optical axis of said verification device substantially lies in a plane defined by said first axis and said third axis or in a plane defined by said second axis and said third axis.
10. The method of claim 7, wherein said step of acquiring said transmission mode image is carried out at a first tilt angle and wherein a further step of acquiring an additional transmission mode image is carried out at a second tilt angle different from said first tilt angle, and wherein said transmission mode image and said additional transmission mode image are used in said step of verifying said authenticity of said security document.
11. The method of claim 7, wherein said tilt angle is greater than 30 degrees.
12. The method of claim 7, wherein said tilt angle is greater than 45 degrees.
13. The method of claim 1, wherein said perforation pattern is self-similar.
14. The method of claim 1, wherein said step of acquiring said reflection mode image comprises a change of an illumination of said security document.
15. The method of claim 14, wherein the change of the illumination of said security document is done by means of a firing of a flash of said verification device.
16. The method of claim 1, wherein a shape of at least one of said perforations, and/or a lateral dimension parallel to a surface of said substrate of at least one of said perforations, and/or a transmitted light intensity and/or wavelength through at least one of said perforations, and/or a number of perforations, and/or an absolute and/or a relative positioning of at least one of said perforations, and/or at least one angle between two connecting lines between three perforations is or are used in said step of verifying said authenticity of said security document.
17. The method of claim 1, wherein said security document additionally comprises at least one perforation which is not used in said step of verifying said authenticity of said security document.
18. The method of claim 1, wherein said security feature is a printed security feature on said substrate.
19. The method of claim 1, comprising a further step of determining a relative alignment of said security document with respect to said verification device, in particular by means of using an acquired image of said security document and by comparing an alignment dependent parameter of said security document in said acquired image to an expected alignment dependent parameter.
20. A verification device for verifying an authenticity of a security document comprising: a camera for acquiring a transmission mode image of at least a part of a perforation pattern of said security document and an analysis and control unit adapted and structured to carry out the step of a method of claim 1.
21. The method of claim 1, wherein at least one of said perforations of said substrate has a lateral dimension less than 150 microns in at least one direction parallel to a surface of said substrate.
22. The method of claim 1, wherein at least one of said perforations of said substrate has a lateral dimension less than 100 microns, in at least one direction parallel to a surface of said substrate.
23. A non-transitory computer-readable medium comprising computer program code that when executed by one or more processors, causes the one or more processors to: acquire by means of a verification device a transmission mode image of at least a part of a perforation pattern in a substrate of a security document, wherein said perforation pattern comprises a plurality of perforations of at least a part of said substrate of said security document, wherein to the naked eye of a human observer at least one of said perforations is not visible in a reflection mode, acquire by means of said verification device a reflection mode image of at least a part of said perforation pattern of said security document, acquire by means of said verification device a reflection mode image and/or a transmission mode image of a security feature of said security document, determine a relative positioning of at least one of said perforations with respect to said security feature, and verify an authenticity of said security document using said transmission mode image of at least said part of said perforation pattern, said reflection mode image of at least said part of said perforation pattern, said reflection mode image and/or said transmission mode image of said security feature, and said determined relative positioning.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The invention and its embodiments will be more fully appreciated by reference to the following detailed description of presently preferred but nonetheless illustrative embodiments in accordance with the present invention when taken in conjunction with the accompanying drawings.
(2) FIG. 1 shows a security document 100 comprising a printed security feature 101 on a flat substrate 200 with perforation patterns 210, 220, 230, and 240 each comprising three perforations 211, 212, 213 extending through the substrate 200,
(3) FIG. 2 shows a projection along y of a sectional view along A-A of FIG. 1's security document 100 lo as well as a light source 400 and a verification device 500 with an analysis and control unit 501 and a camera 502 in a transmission setup,
(4) FIG. 3 shows a different embodiment of a security document 100 comprising a printed security feature 101 on a flat substrate 200 made of three layers 201, 202, and 203 with a perforation pattern 210 comprising three perforations 211, 212, 213 extending through different layers 201, 202, and/or 203 of the substrate 200, and
(5) FIG. 4a shows a top view of a security document 100 comprising a perforation pattern 210 with two line-shaped perforations 211, 212, and with two additional perforations 213 and 213,
(6) FIG. 4b shows a perspective view of the security document 100 of FIG. 4a under a first tilt angle phi_1 around an axis x,
(7) FIG. 4c shows a perspective sectional view along B-B of FIG. 4b,
(8) FIG. 4d shows a perspective view of the security document 100 of FIG. 4a under a second tilt angle phi_2 around an axis y,
(9) FIG. 4e shows a perspective sectional view along C-C of FIG. 4d,
(10) FIGS. 5a, 5b, and 5c show three differently shaped perforations 215, 215, and 215, and
(11) FIG. 6 shows a different embodiment of a security document 100 comprising a flat substrate 200 which is foldable along a line D-D with perforation patterns 210, 220, 230, and 240 each comprising three perforations 216, 217, 218 extending through the substrate 200.
MODES FOR CARRYING OUT THE INVENTION
(12) Description of the Figures:
(13) FIG. 1 shows a security document 100, i.e., a banknote 100, comprising a printed security feature 101 (shown in the bottom part of the figure) on a surface of a flat substrate 200. The flat substrate comprises two .sub.n surfaces that are defined as the two opposing larger faces of the substrate that are perpendicular to the smaller lateral planes of the substrate. The security document 100 furthermore comprises four triangular shaped perforation patterns 210, 220, 230, and 240, each of them comprising three circular perforations 211, 212, 213 (i.e., the whole circles are perforated) extending axially (i.e., along an axis z which is perpendicular to the surfaces of the substrate) through the substrate 200. Here, the term triangular shaped perforation pattern relates to a perforation pattern 210, 220, 230, 240 with a perforation 211, 212, 213 arranged in each corner of an imaginary triangle. In other words, imaginary sides a, b, c of such an imaginary triangle connect the centers of the circular perforations 211, 212, and 213. The angle between the imaginary sides a and b is referred to as , the angle between the sides a and c is referred to as , and the angle between the sides b and c is referred to as .
(14) The circular perforations 211, 212, and 213 have lateral diameters of 100 m and are thus not visible to the naked eye of a human observer in a reflection mode. In the described embodiment, all perforations 211, 212, and 213 have substantially the same shapes and substantially the same lateral dimensions (i.e., along axes x and y parallel to a surface of the substrate 200) and substantially the same axial dimensions (i.e., along z).
(15) The perforation patterns 210, 220, 230, and 240 also have substantially the same shapes and overall dimensions, however, they are rotated and translated with respect to each other. Thus, the perforation patterns 210, 220, 230, and 240 are distributed over the substrate 200.
(16) As it is also described later with respect to FIG. 2, to verify an authenticity of the security document 100, a transmission mode image of at least a part of the perforation patterns 210, 220, 230, and 240 is acquired by means of a verification device 500, e.g., a camera-equipped cellphone. In one embodiment, at least one perforation pattern 210, 220, 230 or 240 needs to be acquired in full to successfully verify the security documents authenticity. Then, the number and the shapes of the perforations 211, 212, and 213 in the acquired transmission mode image are compared to a perforation pattern template which is pre-stored in the verification device. In case of a positive match, the relative positioning of the perforations 211, 212, and 213 with respect to each other, specifically, the lengths of sides a, b, and c as well as the angles a, p, and y are determined and compared to the pre-stored master template. The security document 100 is considered authentic if the determined values and the stored values are within a threshold, e.g., not deviating more than 5%. Suitable image feature recognition algorithms and/or other distinctive features for the above described steps are known to the person skilled in the art. Some examples are, e.g., also published in Lowe, D. G., Distinctive Image Features from Scale-Invariant Keypoints, International Journal of Computer Vision, 60, 2, pp. 91-110, 2004, Suzuki, S. and Abe, K., Topological Structural Analysis of Digitized Binary Images by Border Following, CVGIP 30 1, pp. 32-46, 1985, and/or http://en.wikipedia.org/wiki/Ramer-Douglas-Peucker_algorithm (as accessed on Sep. 5, 2012).
(17) In addition to the perforations 211, 212, and 213, the security document 100 also comprises a randomly distributed plurality of perforations 214 (only two are referenced for clarity) which are not used in the step of verifying the authenticity of the security document 100. Thus, the distinctive features that are used for authenticity verification can be more easily hidden from a potential counterfeiter.
(18) FIG. 2 shows a projection along y of a sects view along A-A of FIG. 1's security document 100. The substrate 200 can be laminated to an optional mounting substrate 208 (dotted) for stability. A light source 400 is arranged on one side of the security document 100 and a verification device 500 with an analysis and control unit 501 and with a camera 502 is arranged on an opposing side of the security document 100. Thus, a transmission mode image of the perforation patterns 210, 220, 230, and 240 can be more easily acquired by means of the verification device 500. Please note that only the perforation patterns 210 and 240 are shown for clarity and that sectioned perforations 213 and 211, respectively, are shown with solid lines whereas projected perforations 211, 212 and 212, 213, respectively, are shown with dotted lines. In addition to the transmission. mode image of the perforation patterns 210, 220, 230, 240, also a reflection mode image of the perforation patterns 210, 220, 230, 240 as well as of the printed security feature 101 is acquired by the verification device 500. For acquiring the reflection mode image, it is ensured that the illumination of the back-surface (first, surface, along +z) of the security document 100 originating from light source 400 is no longer outshining the illumination of the front-surface (second surface, along z) of security document 100. For this, a flash 503 of the verification device 500 is fired during acquiring the reflection mode image but not during acquiring the transmission mode image. Then, both the reflection mode image and the transmission mode image are used for verifying the authenticity of the security document 100. Specifically, a relative positioning of the perforations 211, 212, 213 with respect to the printed security feature 101 is determined and compared to a master-template.
(19) For making the authenticity verification procedure more robust against misalignment, a relative alignment of the security document 100 with respect to the verification device 500 is determined using the acquired images. Specifically, a rotation around z, a distance between the verification device 500 and the security document 100 along z, and an (undesired) tilt around x,y are determined and accounted for by means of image-processing algorithms before comparing the authenticity-related features to templates. Thus, the verification procedure becomes more reliable.
(20) FIG. 3 shows a very similar setup as FIG. 2 with a different embodiment of the security document 100. Specifically, the substrate 200 comprises three layers 201, 202, and 203 with different optical properties (e.g., colors, absorbances) and the perforations 211, 212, and 213 axially extend through different combinations of the layers 201, 202, and 203. Thus, in a transmission mode image, the perforations 211, 212, and 213 exhibit different optical properties (e.g., colors, brightnesses) which are used for verifying the authenticity of the security document 100. Thus, the security of the verification process can be improved.
(21) FIG. 4a shows a top view of a security document 100 comprising a perforation pattern 210 with two line-shaped perforations 211, 212 and with two additional perforations 213, 213. The perforations 211 and 212 have substantially the same perforation widths of 100 m and lengths of 15 mm, but they exhibit different orientations, with respect to the substrate 200 of the security document 100. While the perforation 211 is oriented horizontally, i.e., along a first axis x, the perforation 212 is oriented vertically, i.e., along a second axis y. The perforation 213 is a round perforation with a diameter of 100 m and the perforation 213 is a round perforation with a diameter of 700 m. The perforations are not drawn to scale.
(22) FIG. 4b shows a perspective view of the security document 100 of FIG. 4a under a first tilt angle phi_1 around the first axis x. A light source 400 (dotted) is arranged behind the security document 100, i.e., on the +z side, while a verification device 500 (not shown for clarity) is arranged in front of the security document 100, i.e., on the z side of the security document 100. In this embodiment, the step of acquiring a transmission mode image by means of the verification device 500 for authenticity verification of the security document 100 is carried out a non-zero tilt angle phi_1 of 15 degrees around the first axis x. In other words, the optical axis z of the verification device 500 is tilted by phi_1 with respect to the third axis z of the tilted security document 100. The optical axis z lies in a plane defined by the second axis y and the third axis z. Due to this tilting and the dimensioning and orientation of the perforations 211, 212, 213, and 213, only perforations 212 and 213 appear as a bright line and a bright spot (solid lines in the figure), respectively, in the transmission mode image whereas perforations 211 and 213 (dotted lines in the figure) remain substantially dark in transmission mode. Thus, a very specific tilt angle dependent security feature improves the security of the authenticity verification step.
(23) FIG. 4c shows a perspective sectional view of the security document 100 of FIG. 4b along B-B. The original untilted positioning of the security document 100 as shown in FIG. 4a is shown in dotted lines for comparison.
(24) FIG. 4d shows a perspective view of the security document 100 of FIG. 4a under a second tilt angle phi_2 around an axis y. This description above with regard to FIG. 4b similarly pertains to FIG. 4d with the difference that this time, due to the tilting around the second axis y and the dimensioning and orientation of the perforations 211, 212, 213, and 213, only perforations 211 and 213 appear as a bright line and a bright spot (solid lines in the figure), respectively, in the transmission mode image whereas perforations 212 and 213 (dotted lines in the figure) remain substantially dark.
(25) FIG. 4e shows a perspective sectional view of the security document 100 of FIG. 4d along C-C. The original untilted positioning of the security document 100 as shown in FIG. 4a is shown in dotted lines for comparison.
(26) An acquisition of two transmission mode images, one image under a tilt angle phi_1 as described above with regard to FIGS. 4b and 4c and another additional transmission mode image under a tilt angle phi_2 as described above with regard to FIGS. 4d and 4e further improves the security of the authenticity verification step.
(27) FIGS. 5a, 5b, and 5c show three differently shaped perforations 215, 215, and 215. Specifically, perforation 215 of FIG. 5a is substantially Swiss-Cross-shaped and has total up-to-down and left-to-right elongations (as observed in the figure in a normal reading position) of 800 microns with a vertical diameter of the horizontal bar of 300 microns. FIG. 5b shows a free-line perforation 215 with a line diameter of 200 microns. FIG. 5c shows a star-shaped perforation 215 with a total line dimension of 700 microns. Unlike in the perforations 215 and 215 of FIGS. 5a and 5b, not the whole interior part (i.e., line width) of perforation 215 is perforated but here, it is rastered by a quadratic line pattern (black lines) with perforated line widths of 50 microns. With such a perforation, an unperforated mounting substrate 208 can be used for stability (not shown). Such very specific perforations that can be tilt angle dependent improve the security of the authenticity verification step.
(28) FIG. 6 shows a different embodiment of a security document 100 comprising a flat substrate 200 which is partly folded along a line D-D. The line D-D is arranged such that the substrate 200 is divided into two parts 200a and 200b. Perforation patterns 210, 220, 230, 240, and 250 comprising three perforations each are arranged at different locations in said substrate. Furthermore, additional perforations 219 are arranged in the substrate 200. To verify the authenticity of this embodiment of the security document 100, a transmission mode image is acquired by means of the verification device 500 in a fully folded position of the substrate 200 along line D-D (curved arrow), i.e., such that the two folded parts 200a and 200b of the substrate touch each other. Thus, some of the perforations (dotted lines) axially (i.e., along z) coincide with each other and light from the light source 400 is transmitted through the coinciding perforations. By folding the substrate 200 and acquiring a transmission mode image, the original starry sky pattern of the perforations of the original security document is thinned in a way that a smaller number of bright regions appear in a transmission mode image, i.e., only axially coinciding perforations. Thus, the security of the authenticity verification step is improved.
(29) As another option, it would also be possible to align a stencil with perforations or one or more other security documents with specific perforation patterns with the first security document to thin the starry sky pattern of the first security document.
(30) Note:
(31) It should be noted that it is also possible to use shadowing effects to further enhance the security of the authenticity verification step. Specifically, the light distribution from the light source illuminating the first surface of the substrate for acquiring the transmission mode image can be spatially modulated and comprise dark regions. If such a dark region coincides with a perforation, this perforation would appear as a dark spot in the transmission mode image. Then, the contrast of this dark spot compared to the surrounding brighter region of the substrate could be detected and used for is authenticity verification.
(32) 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 practiced within the scope of the following claims.
