Authenticating media signals by adjusting frequency characteristics to reference values

• US 20020031240A1
• Filed: 12/06/2000
• Published: 03/14/2002
• Est. Priority Date: 09/11/2000
• Status: Active Grant

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Levy, Kenneth L., Tian, Jun
• Granted Patent: US 7,346,776 B2
• Time in Patent Office: Days
• US Class Current: 382/100
• CPC Class Codes: G06T 1/0028 Adaptive watermarking, e.g. Human Visual System [HVS]-based watermarking
• CPC Class Codes: G06T 1/0042 Fragile watermarking, e.g. so as to detect tampering
• CPC Class Codes: G06T 1/0071 using multiple or alternating watermarks
• CPC Class Codes: G06T 1/0085 Time domain based watermarking, e.g. watermarks spread over several images
• CPC Class Codes: G06T 2201/0052 Embedding of the watermark in the frequency domain
• CPC Class Codes: H04L 67/06 specially adapted for file transfer, e.g. file transfer protocol [FTP]
• CPC Class Codes: H04L 69/329 in the application layer [OSI layer 7]
• CPC Class Codes: H04L 9/40 Network security protocols
• 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 1/32154 Transform domain methods H04N1/32309 takes precedence
• CPC Class Codes: H04N 1/3216 using Fourier transforms
• CPC Class Codes: H04N 17/004 for digital television systems
• CPC Class Codes: H04N 21/4425 Monitoring of client processing errors or hardware failure
• CPC Class Codes: H04N 21/8358 involving watermark protecting executable software by watermarking G06F21/16; image watermarking in general G06T1/0021; watermarks inserted in still images for transmission purposes H04N1/32144; inserting watermarks during video coding H04N19/467

Abstract

A method of authenticating a media signal and related software, systems and applications. The method transforms at least a portion of the media signal into a set of frequency coefficients in a frequency domain. For example, it applies a Fast Fourier Transform (FFT) or other frequency transform to blocks of a media signal, such as an image, audio or video signal. It adjusts a relationship between selected frequency coefficients to a reference value. This adjustment is selected so that an alteration to be detected, such as a re-sampling operation or digital to analog—analog to digital conversion, alters the relationship. To detect the alteration, a detector computes the relationship in a potentially corrupted version of the signal. It then compares the result with a threshold value to detect whether the alteration has occurred.

Claims

1. A method of authenticating a media signal comprising:

transforming at least a portion of the media signal into a set of frequency coefficients in a frequency domain;

adjusting a relationship between selected frequency coefficients to a reference value such that an alteration to the media signal to be detected alters the relationship.

2. The method of claim 1 wherein the media signal is an image signal.

3. The method of claim 2 wherein the alteration to be detected is scanning, printing or photocopying the image signal.

4. The method of claim 1 wherein the relationship comprises a ratio between a selected coefficient and one or more neighboring coefficients.

5. The method of claim 4 wherein the relationship comprises a ratio between the magnitude of a selected coefficient and an average of neighboring coefficients.

6. The method of claim 1 including:

embedding a calibration signal into the media signal to enable a detector to compensate for changes in scale or translation of the media signal after being adjusted according to the relationship.

7. A computer readable medium on which is stored software for performing the method of claim 1.

8. A detector for authenticating a media signal that has been processed according to the method of claim 1.

9. The detector of claim 1 including means for computing the relationship in a potentially corrupted version of the media signal and comparing the relationship with a threshold to detect alteration of the potentially corrupted media signal.

10. A method of authenticating a media signal comprising:

evaluating signal peaks at selected frequency coefficients of the media signal, where the media signal has been previously modified to include peaks at the selected frequencies; and

determining based on degradation of the signal peaks whether the media signal has been altered.

11. The method of claim 10 including using one or more of the peaks to re-orient the media signal.

12. The method of claim 10 including:

correlating the media signal with a calibration signal having an arrangement of peaks at selected frequency coefficients to determine translation and scale of the media signal.

13. The method of claim 12 including:

correlating the media signal with the calibration signal to determine rotation of the media signal.

14. The method of claim 10 wherein the media signal is an image.

15. The method of claim 10 wherein the media signal is an audio signal.

16. The method of claim 10 wherein the media signal is a video signal.

17. A computer readable medium having software for performing the method of claim 10.

19. The decoder of claim 18 wherein the detector and analyzer use at least some of the same frequency coefficients for determining orientation and evaluating whether the media signal has been altered.

20. The decoder of claim 18 wherein the analyzer is used to detect reproduction of a printed image by examining degradation of the media signal at selected frequency coefficients.

18. A watermark decoder comprising:

a detector for correlating a calibration signal with a media signal suspected of carrying a watermark to determine orientation parameters describing orientation of the media signal at embedding of the watermark, where the calibration signal includes a set of peaks at selected frequency coefficients; and

an analyzer operable to orient the media signal using the orientation parameters and to evaluate whether the media signal has been altered after the embedding by examining signal peaks at selected frequency coefficients in the media signal.