Method and apparatus for detecting a watermark in a manipulated image

• US 6,671,388 B1
• Filed: 09/25/2000
• Issued: 12/30/2003
• Est. Priority Date: 09/27/1999
• Status: Expired due to Term

• Current Assignee: Nagravision SA (Kudelski SA)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Haitsma, Jaap Andre, Kalker, Antonius Adrianus Cornelis Maria, Op De Beeck, Marc Joseph Rita
• Primary Examiner(s): Johns, Andrew W.
• Application Number:
  US09/670,006
• Time in Patent Office: 1,191 Days
• Field of Search: 382/100, 382/232, 382/278, 382/286, 382/289, 382/290, 382/291, 382/292, 382/293, 382/295, 382/296, 382/298, 382/301, 380/210, 380/252, 380/287, 380/54, 713/176
• US Class Current: 382/100
• CPC Class Codes: G06T 1/0064 Geometric transfor invariant watermarking, e.g. affine transform invariant
• CPC Class Codes: G06T 1/0071 using multiple or alternating watermarks
• CPC Class Codes: G06T 2201/0065 Extraction of an embedded watermark; Reliable detection
• CPC Class Codes: H04N 1/32149 Methods relating to embedding, encoding, decoding, detection or retrieval operations
• CPC Class Codes: H04N 1/32293 Repeating the additional information in a regular pattern
• CPC Class Codes: H04N 1/32352 Controlling detectability or arrangements to facilitate detection or retrieval of the embedded information, e.g. using markers for decoding, detection or retrieval operations H04N1/32149 and subgroups take precedence
• CPC Class Codes: H04N 2201/3233 of authentication information, e.g. digital signature, watermark
• CPC Class Codes: H04N 2201/327 which are undetectable to the naked eye, e.g. embedded codes

Abstract

Most watermarking schemes are not resistant to geometric distortions of a watermarked image, because such manipulations destroy the correlation between the original watermark and the watermark in the manipulated image. In order to restore the correlation, a suspect image (Q) is analyzed (6) for the presence of a repeated data pattern. If such a pattern is found, it is concluded that the image has been watermarked by “tiling” a small-sized watermark pattern over the extent of the image. The actual detection of whether the watermark is a given watermark W is subsequently performed by determining the periodicity of the pattern found in the suspect image, and processing (9) the suspect image so as to match the periodicity of the processed image with the given periodicity of the watermark to be detected. If the suspect image indeed includes the given watermark W, the geometric manipulation is thereby undone and a conventional watermark detector (3) will signify this accordingly. If a combination of operations can generate the same periodicity, the detection step will include the set of possible combinations.

Claims

1. A method of detecting a watermark in a suspect image, said method comporising the steps:

detecting whether said suspect image includes a periodically repeated embedded data pattern; and

concluding that said periodically repeated data pattern represents an embedded watermark,

wherein said method further comprises the steps;

determining the periodicity of said data pattern;

applying a given watermark having a given periodicity;

processing the suspect image or the given watermark so as to match the periodicity of the data pattern in the processed suspect image with the periodicity of the processed given watermark; and

detecting whether the data pattern in the processed suspect image corresponds to the processed given watermark,

and wherein the step of processing the suspect image or the given watermark is repeated for a finite set of predetermined processing operations.

2. The method as claimed in claim 1, wherein the step of processing the suspect image or the given watermark comprises subjecting the suspect image or the given watermark to an affine transform operation.

3. An arrangement for detecting a watermark in a suspect image, said arrangement comprising:

means for detecting whether said suspect image includes a periodically repeated embedded data pattern; and

means for concluding that said periodically repeated data pattern represents an embedded watermark,

wherein said arrangement further comprises;

means for determining the periodicity of said data pattern;

means for applying a given watermark having a given periodicity;

means for processing the suspect image or the given watermark so as to match the periodicity of the data pattern in the processed suspect image with the periodicity of the processed given watermark; and

means for detecting whether the data pattern in the processed suspect image corresponds to the processed given watermark,

and wherein the means for processing the suspect image or the given watermark repeatedly performs said processing for a finite set of predetermined processing operations.

4. The arrangement as claimed in claim 3, wherein the means for processing the suspect image or the given watermark subjects the suspect image or the given watermark to an affine transform operation.