Authenticating media signals by adjusting frequency characteristics to reference values
First Claim
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.
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Accused Products
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.
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Citations
20 Claims
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1. A method of authenticating a media signal comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of authenticating a media signal comprising:
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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. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 19, 20)
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18. A watermark decoder comprising:
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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.
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Specification