Secure Documents With Hidden Signals, and Related Methods and Systems

• US 20080130945A1
• Filed: 10/23/2007
• Published: 06/05/2008
• Est. Priority Date: 05/08/1995
• Status: Active Grant

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Rhoads, Geoffrey B., Rodriguez, Tony F.
• Granted Patent: US 7,555,139 B2
• Time in Patent Office: Days
• US Class Current: 382/100
• CPC Class Codes: G06T 1/0064 Geometric transfor invariant watermarking, e.g. affine transform invariant
• CPC Class Codes: G06T 2201/0052 Embedding of the watermark in the frequency domain
• CPC Class Codes: H04N 1/32144 embedded in the image data, i.e. enclosed or integrated in the image, e.g. watermark, super-imposed logo or stamp
• CPC Class Codes: H04N 1/32203 Spatial or amplitude domain methods H04N1/32309 takes precedence
• CPC Class Codes: H04N 1/32309 in colour image data
• CPC Class Codes: Y10S 283/902 Anti-photocopy

Abstract

A security document comprising artwork including a security pattern, characterized in that the security pattern has the form of a line structure in which lines width or line spacing is adjusted to carry predefined data. The artwork is generated by the modifying at least one color of at least a part of the artwork to embed the security pattern in the artwork. Methods for detecting the security pattern include use of a frequency domain structure to detect the security pattern despite rotation and scaling of the document, use of signal tiling to improve signal detection, and use of statistical analyses to verify detection of the security pattern.

Claims

1. A printed security document, the security document comprising artwork including a security pattern, characterized in that the security pattern has the form of a line structure in which line width and/or line spacing is adjusted to carry predefined data, the artwork is generated by the modifying at least one color of at least a part of the artwork to embed the security pattern in the artwork.

2. The printed security document of claim 1 wherein the security pattern is repeated in blocks across the security document.

3. The printed security document of claim 1 wherein the security pattern includes a pattern in a frequency transform domain that enables reading of the predefined data despite rotation of the security document.

4. The printed security document of claim 1 wherein the security pattern includes a pattern in a frequency transform domain that enables reading of the predefined data despite spatial scaling of the security document.

5. The printed security document of claim 1 wherein the predefined data conveys a device control signal to control reproduction of the printed security document.

20. An article of currency according to claim 1.

6. A method of generating artwork for a security document, the method comprising:

providing a security pattern modulated to carry predefined data; and

modifying width or line spacing of the artwork of the security document according to the security pattern, wherein the artwork is generated by the modifying at least one color of at least a part of the artwork to embed the security pattern in the artwork.

7. The method of claim 6 wherein the security pattern includes a pattern in a frequency transform domain that enables detection of the predefined data despite rotation of the security document.

8. The method of claim 6 wherein the security pattern includes a pattern in a frequency transform domain that enables detection of the predefined data despite spatial scaling of the security document.

9. The method of claim 6 wherein the security pattern is repeated in blocks across the artwork.

10. The method of claim 6 wherein the predefined data signals a device to control reproduction of an image of the security document.

11. The method of claim 6 including:

performing an inverse transform of a frequency domain pattern to produce at least a portion of the security pattern.

12. The method of claim 11 wherein the frequency domain pattern enables detection of the predefined data despite rotation of the security document.

13. A method of detecting a security pattern embedded in a security document, the method comprising:

performing a frequency domain transform of artwork in the security document, the line width or spacing of line structures of the artwork being modified to incorporate the security pattern; and

correlating the transformed artwork with a predefined signal to detect the security pattern, the security pattern having frequency domain attributes enabling detection of the security pattern despite rotation of the security document.

14. The method of claim 13 including performing plural statistical analyses to detect the presence of the security pattern in the artwork.

15. The method of claim 13 including combining blocks of the artwork in which the security pattern has been repeated to improve detection of the security pattern.

16. A method of detecting a security pattern embedded in a security document, the method comprising:

analyzing artwork to detect the security pattern in modifications of the line width or spacing of line structures of the artwork; and

performing plural statistical analyses on the detected security pattern to read predefined data carried in the security pattern.

17. The method of claim 16 including performing a transform domain, and detecting the security pattern in the transform domain, the security pattern including a pattern in the frequency domain that enables detection of the security pattern despite rotation.

18. A printed document, the document comprising artwork including a pattern, characterized in that the security pattern has the form of a line structure in which lines are drawn in a manner that modulates at least one color of the artwork to carry predefined data, the artwork is generated by the modifying at least one color of at least a part of the artwork to embed the pattern in the artwork.

19. A printed article, characterized by inclusion of a machine-detectable signal represented in a marking formed on the surface of said article, the signal being based on a rotationally symmetric pattern and being machine-detectable from visible light scan data taken from said article, but said signal being imperceptible upon human inspection of said article, said signal indicating to a compliant apparatus that said article should not be reproduced.

21. The article of claim 19 wherein said marking comprises a series of lines that also define aesthetic artwork on said article, said lines being varied in width or location to represent said signal.

22. A method of sensing and responding to a hidden signal embodied on a printed article, the method including:

collecting visible light scan data from the article;

transforming the scan data to a complementary domain;

inspecting the transformed data for a telltale pattern, said telltale pattern being rotationally symmetric, wherein presence of said pattern indicates presence of said signal; and

taking an action based on presence of said signal.

23. The method of claim 22 in which the telltale pattern comprises plural concentric rings.

24. The method of claim 22 that includes filtering the transformed scan data prior to inspecting same for the telltale pattern.

25. The method of claim 22 in which said transforming generates transform data based on a Fourier transform.

26. A method of representing a signal in a printed document, so that the signal can readily be machine-sensed from visible light scan data acquired from the document no matter what orientation the document is in when the scan data is acquired, characterized by printing the document with a pattern that hides the signal as a subtle noise-like pattern that modulates width or placement of lines defining line art on said document, said noise-like pattern being derived from a rotationally symmetric pattern, wherein presence of said pattern in a printed document serves to indicate to compliant apparatus that the document should not be reproduced.

27. In an system that processes visible light scan data acquired from a printed line art document, an improved method of operation including:

analyzing said scan data to detect a control signal steganographically represented by variations in width or placement of lines comprising the line art; and

taking an action in response to detection of the control signal.

28. The method of claim 27 wherein the analyzing includes transforming the scan data to a complementary signal domain, and detecting a pattern in the transformed data.

29. The method of claim 28 in which said transforming generates transform data based on a Fourier transform.

30. A printed line art document having a pattern formed over at least a portion thereof, characterized in that the pattern hides a signal that indicates, to compliant equipment, that the document should not be copied, the signal-hiding pattern being detectable by computer analysis of visible light scan data corresponding to said document, the pattern being based on a rotationally symmetric feature.

31. The document of claim 30, wherein the pattern yields a distinctive pattern when transformed to a complementary domain.

32. The document of claim 30, wherein the pattern yields a distinctive pattern when processed with a transform of a Fourier type.

33. The document of claim 30 wherein said pattern is represented by variations in width or placement of lines comprising said line art.