Apparatus and methods for improving detection of watermarks in content that has undergone a lossy transformation
First Claim
1. A method of obtaining information about a first digital representation of a sequence of images that may be derived from a second digital representation of the sequence of images, the second digital representation having a watermark embedded therein and the method comprising the steps of:
- extracting a first watermark vector from a portion of the first digital representation that corresponds to a portion of the second digital representation in which the watermark is embedded;
obtaining a second watermark vector that is a replica of the watermark'"'"'s watermark vector; and
computing a similarity of the first watermark vector with the second watermark vector.
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Abstract
Techniques for improving detection of watermarks in content that has undergone a lossy transformation. One of the techniques is used when the message that is contained in a watermark belonging to a digital representation that is derived from an original watermarked digital representation cannot be decoded. The technique obtains information about the watermark by comparing the watermark vector for the watermark that cannot be decoded with a replica of the watermark vector from the original watermarked digital representation. The replica is made using the message. Depending on the degree of similarity, the watermark'"'"'s presence and some of its characteristics may be determined. Another technique improves the robustness of watermarks that are used for authentication by employing a short (even single-bit) watermark vector to make the watermark and using the message needed for the authentication to determine where the watermark is located in the digital representation. Authentication of a digital representation is done by determining whether the watermark is present in the digital representation. In another technique, detection of the presence of a watermark is used to determine what areas of a digital representation have been subject to alteration. Techniques for synchronizing digital representations for watermark detection and other purposes include adding marks whose locations can be automatically detected only with the help of information that is external to the digital representation, such as a key, and adding marks to a sequence of digital representations and detecting the marks by summing the sequence.
110 Citations
18 Claims
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1. A method of obtaining information about a first digital representation of a sequence of images that may be derived from a second digital representation of the sequence of images, the second digital representation having a watermark embedded therein and the method comprising the steps of:
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extracting a first watermark vector from a portion of the first digital representation that corresponds to a portion of the second digital representation in which the watermark is embedded;
obtaining a second watermark vector that is a replica of the watermark'"'"'s watermark vector; and
computing a similarity of the first watermark vector with the second watermark vector. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A method of watermarking a first digital representation of a sequence of images, the method comprising the steps of:
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adding a watermark to the digital representation, the locations at which the watermark is embedded in the digital representation being determined at least in part by a message; and
making the message available to determine locations in a second digital representation of a sequence of images, the second digital representation being possibly derived from the first digital representation and the locations being locations at which the watermark can be expected to be embedded.
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18. A method of determining whether a particular digital representation of a sequence of images is derived from a watermarked digital representation of the sequence of images whose watermark was embedded at locations determined at least in part by a message, the method comprising the steps of:
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obtaining the message;
using the message to determine the locations at which the watermark cam be expected to be embedded in the particular representation; and
determining from values at the determined locations whether the watermark is present in the particular digital representation.
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Specification