Watermarks carrying content dependent signal metrics for detecting and characterizing signal alteration

• US 6,512,837 B1
• Filed: 10/11/2000
• Issued: 01/28/2003
• Est. Priority Date: 10/11/2000
• Status: Expired due to Term

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Ahmed, Farid
• Primary Examiner(s): Johns, Andrew W.
• Application Number:
  US09/689,250
• Time in Patent Office: 839 Days
• Field of Search: 382/100, 382/232, 380/210, 380/252, 380/287, 380/54, 713/176
• 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 1/0064 Geometric transfor invariant watermarking, e.g. affine transform invariant
• CPC Class Codes: G06T 2201/0061 Embedding of the watermark in each block of the image, e.g. segmented watermarking
• 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
• CPC Class Codes: H04N 1/00039 Analysis, i.e. separating and studying components of a greater whole
• CPC Class Codes: H04N 1/00045 using a reference pattern designed for the purpose, e.g. a test chart
• 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 1/32229 with selective or adaptive application of the additional information, e.g. in selected regions of the image H04N1/32213 takes precedence
• CPC Class Codes: H04N 1/32288 Multiple embedding, e.g. cocktail embedding, or redundant embedding, e.g. repeating the additional information at a plurality of locations in the image

Abstract

The invention provides methods and systems for detecting and characterizing alterations of media content, such as images, video and audio signals, using watermark messages to carry signal metrics. By comparing signal metrics extracted from the watermark to signal metrics calculated from a suspect signal, a watermark decoder can detect and even classify types of alterations to the watermarked signal.

Claims

1. A method of detecting alteration of a watermarked media signal comprising:

dividing the watermarked media signal into blocks;

decoding watermark signals from the blocks;

extracting signal metrics from the watermark signals decoded from the blocks;

comparing the signal metrics with corresponding signal metrics computed from the watermarked media signal, wherein a difference between the computed and extracted signal metrics evidences signal alteration;

wherein results of comparing the signal metrics are used to characterize a type of alteration based on a model that maps signal metric changes to alteration types.

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

3. The method of claim 1 wherein signal metrics are computed for blocks of the media signal such that each block has two or more corresponding signal metrics.

4. The method of claim 3 wherein the signal metrics are computed from and embedded into the same blocks.

5. The method of claim 1 wherein there are at least three metrics, and one metric is a function of two other metrics.

6. The method of claim 1 wherein at least one metric is computed based on edge information in a block of the media signal.

7. The method of claim 6 wherein the media signal comprises an image signal, and at least one metric is compute based on horizontal and vertical edge information.

8. A computer readable medium having software for performing the method of claim 1.

9. A method of detecting alteration of a watermarked media signal comprising:

dividing the watermarked media signal into blocks;

decoding watermark signals from the blocks;

extracting signal metrics from the watermark signals decoded from the blocks;

comparing the signal metrics with corresponding signal metrics computed from the watermarked media signal, wherein a difference between the computed and extracted signal metrics evidences signal alteration;

wherein at least one metric is computed based on differences between adjacent blocks of the media signal.

10. A method of detecting alteration of a watermarked media signal comprising:

dividing the watermarked media signal into blocks;

decoding watermark signals from the blocks;

extracting signal metrics from the watermark signals decoded from the blocks;

comparing the signal metrics with corresponding signal metrics computed from the watermarked media signal, wherein a difference between the computed and extracted signal metrics evidences signal alteration;

wherein a first metric is a function of media signal data in a block, and a second metric is a function of differences between the media signal data of adjacent blocks.

11. The method of claim 10 wherein a third metric is a function of the first and second metrics.

12. A method of detecting alteration of a watermarked media signal comprising:

dividing the watermarked media signal into blocks;

decoding watermark signals from the blocks;

extracting signal metrics from the watermark signals decoded from the blocks;

comparing the signal metrics with corresponding signal metrics computed from the watermarked media signal, wherein a difference between the computed and extracted signal metrics evidences signal alteration;

wherein the metrics include horizontal and vertical edge information metrics, and a change in the horizontal and vertical edge information metrics is used to detect copying.

13. A method for embedding auxiliary information into a media signal for detecting alteration of the media signal, the method comprising:

calculating two or more signal metrics of the media signal; and

performing a watermark embedding process to embed the signal metrics into the media signal, such that the signal metrics are within an acceptable tolerance when computed from the media signal before and after the watermark embedding process;

wherein the signal metrics are selected to detect particular types of alteration and are part of parametric model that classifies the particular types of alteration as a function of the signal metrics.

14. The method of claim 13 including computing the metrics for each of block of a set of blocks of the media signal, and encoding the signal metrics for each block into the media signal.

15. The method of claim 14 wherein the signal metrics are embedded into the same blocks from which they are derived.

16. The method of claim 13 wherein one of the signal metrics is based on edge information of the media signal.

17. A computer readable medium having software for performing the method of claim 15.

18. A method for embedding auxiliary information into a media signal for detecting alteration of the media signal, the method comprising:

calculating two or more signal metrics of the media signal; and

performing a watermark embedding process to embed the signal metrics into the media signal, such that the signal metrics are within an acceptable tolerance when computed from the media signal before and after the watermark embedding process;

wherein the signal metrics include a signal metric derived from differences between adjacent blocks of the media signal and embedded into one of the adjacent blocks.