Fragile and emerging digital watermarks

• US 20050041835A1
• Filed: 04/29/2004
• Published: 02/24/2005
• Est. Priority Date: 07/02/2001
• Status: Active Grant

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Reed, Alastair M., Sharma, Ravi K., Rodriguez, Tony F.
• Granted Patent: US 8,094,869 B2
• Time in Patent Office: Days
• US Class Current: 382/100
• CPC Class Codes: G06T 1/0042 Fragile watermarking, e.g. so as to detect tampering
• CPC Class Codes: H04N 1/00002 Diagnosis, testing or measuring; Detecting, analysing or monitoring not otherwise provided for error detection, error correction or monitoring in digital computers or digital computer components G06F11/00
• CPC Class Codes: H04N 1/00005 relating to image data
• CPC Class Codes: H04N 1/00037 Detecting, i.e. determining the occurrence of a predetermined state H04N1/00031 takes precedence

Abstract

This disclosure describes methods for using embedded auxiliary signals in documents for copy detection. In one implementation we embed an auxiliary signal with a first color that is out of gamut with process color inks or with a particular range of printers. A process color approximation of the first color yields a relatively different contrast when, e.g., viewed with an interference filter. A copy is determined based on the relative presence or absence of the auxiliary signal. In another implementation, we provide a first auxiliary signal with a first color and a second auxiliary signal with a second color. A filter is matched according to the spectral response of the first color. The second color preferably includes a spectral response that is inversely related to the matched filter. The first signal is then detectable in a process color copy, but less so in the original. However, the second signal is detectable in the original, but less so in the copy. In still other implementations we compare relative contrast of a signal to determine an original from a copy.

Claims

1. A method for analyzing an image of a printed object to determine whether the printed object is a copy or an original, said method comprising:

analyzing a machine readable auxiliary signal that is embedded in the image, wherein the auxiliary signal is embedded at embedding locations using a print structure that changes in response to a copy operation, the change causing a convergence of a characteristic such that the machine readable signal becomes more detectable; and

based on evaluating the machine readable auxiliary signal, determining whether the printed object is a copy or an original.

2. The method of claim 1 wherein the print structure includes a first spot color.

3. The method of claim 2, wherein the spot color is approximated by a copy operation using a plurality of process color inks.

4. The method of claim 3 wherein the spot color corresponds to a spot color ink that is out of gamut with respect to the process color inks.

5. The method of claim 4, wherein the process color inks comprise cyan ink, magenta ink and yellow ink.

6. The method of claim 5, wherein the process color inks further comprise black ink.

7. The method of claim 3, wherein the characteristic comprises relative contrast.

8. The method of claim 7, wherein the process color inks provide relatively more contrast than the spot color.

9. The method of claim 7, wherein the process inks provide a first contrast when emphasized relative to a second contrast provided by the spot color when similarly emphasized.

10. The method of claim 7, wherein the image is captured through an emphasizer.

11. The method of claim 10, wherein the emphasizer comprises an interference filter.

12. The method of claim 10, wherein the emphasizer comprises selective illumination.

13. The method of claim 10, wherein the emphasizer comprises a contrast enhancer.

41. The method of claim 1, wherein the machine readable auxiliary signal comprises digital watermarking.

14. A method for analyzing a printed object to determine whether the printed object is a copy or an original, said method comprising:

imaging the printed object with an emphasizer including transmission characteristics, wherein the printed object comprises a first machine readable auxiliary signal conveyed with a first color including a spectral response that is inversely related to the transmission characteristics of the emphasizer, the printed object further comprising a second machine readable auxiliary signal embedded therein, wherein the second machine readable auxiliary signal is conveyed with a second color including a spectral response that corresponds to the transmission characteristics of the emphasizer; and

based on the detection of at least one of the first machine-readable auxiliary signal and the second machine-readable auxiliary signal, determining whether the printed object is a copy or an original.

15. The method of claim 14, wherein the printed object is determined to be an original when the first machine-readable auxiliary signal is detectable at a predetermined level.

16. The method of claim 14, wherein the printed object is determined to be a copy when the second machine-readable auxiliary signal is detectable at a predetermined level.

17. The method of claim 14, wherein the printed object is determined to be an original when the first machine-readable auxiliary signal is detectable at a predetermined level, and the second machine-readable auxiliary signal is at least one of undetectable and detectable but below a predetermined threshold.

18. The method of claim 14, where the first color comprises a first spot color and the second color comprises a second, different spot color.

19. The method of claim 18, wherein a copy is produce through an operation that approximates each of the first spot color and the second spot color with process color inks.

20. The method of claim 19, wherein the emphasizer comprises an interference filter.

21. The method of claim 19, wherein the emphasizer comprises selective illumination.

22. The method of claim 19, wherein the emphasizer comprises a color contrast enhancer.

42. The method of claim 14, wherein the first machine readable auxiliary signal and the second machine readable auxiliary signal comprise digital watermarking.

23. A method to determine whether a printed object is a copy or an original, the printed object comprising a first machine readable auxiliary signal conveyed with a first color, the first color including a first spectral response, wherein the printed object further comprises a second machine readable auxiliary signal conveyed with a second color, the second color including a second, different spectral response, said method comprising:

emphasizing contrast of the first color and second color relative to a white background in an image captured of the printed object; and

based on a detection reading of at least one of the first machine-readable auxiliary signal and the second machine-readable auxiliary signal, determining whether the image corresponds to an image of the original printed object or copy of the original printed object.

24. The method of claim 23, wherein the first color comprises a first spot color and the second color comprises a second spot color.

25. The method of claim 23, wherein a copy is made by a process color approximation of the first spot color and the second spot color, with at least one of the first spot color and the second spot color being out of gamut with respect to the process color inks.

26. The method of claim 25, wherein the first spot color is out of gamut, and wherein the contrast of the first spot color is emphasized so that the first machine-readable auxiliary signal is less detectable in an original in comparison to the process color ink approximation of the first auxiliary signal in a copy.

27. The method of claim 26, wherein the second spot color is also out of gamut, and wherein the contrast of the second spot color is emphasized so that the second machine-readable auxiliary signal is more detectable in the original in comparison to a similarly emphasized process color ink approximation of the second auxiliary signal in a copy.

28. A method for analyzing a printed object to determine whether the printed object is a copy or an original, said method comprising:

receiving optical scan data associated with the printed object, the optical scan data being captured with an emphasizer including transmission characteristics, wherein the printed object comprises a first image embedded therein with a first color including a spectral response that is inversely related to the transmission characteristics of the emphasizer, the printed object further comprising a second image embedded therein, wherein the image is embedded with a second color including a spectral response that corresponds to the transmission characteristics of the emphasizer; and

based on the visual detection of at least one of the first image and the second image, determining whether the printed object is a copy or an original.

29. The method of claim 28, wherein the first image and the second image are visually imperceptible without the effects of the emphasizer.

30. A method for analyzing an image of a printed object to determine whether the printed object is a copy or an original, the method comprising:

determining whether at least one of a first machine readable auxiliary signal and a second machine readable auxiliary signal is embedded in the image, wherein the first auxiliary signal is conveyed using a first color and the second auxiliary signal is conveyed using a second color, the first and second colors being represented differently in response to a copy operation, the different representation providing a divergence or convergence of a characteristic of the colors such that the machine readable signals becomes more or less detectable; and

based on evaluating the machine-readable auxiliary signals, determining whether the printed object is a copy or an original.

31. The method of claim 30, wherein the first color comprises a first spot color, and the second color comprises a second spot color.

32. The method of claim 31, wherein the copy operation comprises a first approximation of the first spot color with process color inks and a second approximation of the second spot color with process color inks.

33. The method of claim 32, wherein the characteristic comprises relative contrast.

34. The method of claim 33, wherein the first approximation provides enhanced contrast convergence in comparison to the first spot color when imaged with a filter that is matched to the spectral response of the first spot color.

35. The method of claim 33, wherein the first approximation provides enhanced contrast convergence in comparison to the first spot color when image with illumination that is matched to the spectral response of the first spot color.

36. The method of claim 34, wherein the second approximation provides contrast divergence in comparison to the second spot color when imaged with a filter that is inversely matched to the spectral response of the second spot color.

37. The method of claim 34, wherein the second approximation provides contrast divergence in comparison to the second spot color when imaged with illumination that is inversely matched to the spectral response of the second spot color.

38. A printed document comprising:

a nascent digital watermark conveyed on a surface of the printed document with a first set of print structures; and

a fragile digital watermark conveyed on the surface of the printed document with a second set of print structure,

wherein the fragile digital watermark is more detectable relative to the nascent digital watermark in the printed document, whereas the nascent digital watermark is more detectable in a copy of the printed document relative to the fragile digital watermark.

39. The printed document of claim 38, wherein the first set of print structures comprises a first color.

40. The printed document of claim 39, wherein the second set of print structures comprises a second color.