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 second watermark vector belonging to a second watermark embedded therein and the method comprising the steps of:
- an apparatus performing the following;
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 second watermark vector is embedded;
obtaining a comparison watermark vector that is a replica of the second watermark vector;
computing a degree of similarity of the first watermark vector with the comparison watermark vector; and
using the degree of similarity to determine a relationship between the first watermark vector and the second watermark vector, the determined relationship not being based on whether the degree of similarity indicates a match between the first watermark vector and the comparison watermark vector;
wherein the step of extracting a first watermark vector includes synchronizing at least the portion of the first digital representation with the portion of the second digital representation, wherein the second digital representation includes synchronization marks that are locatable in the second digital representation using a secret key, wherein the secret key is used to locate the synchronization marks in the first digital representation which are used to synchronize at least the portion of the first digital representation.
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Abstract
Techniques for watermarking sequences of digital representations and detecting the watermarks in the digital representations. 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 (eve 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.
102 Citations
11 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 second watermark vector belonging to a second watermark embedded therein and the method comprising the steps of:
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an apparatus performing the following; 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 second watermark vector is embedded; obtaining a comparison watermark vector that is a replica of the second watermark vector; computing a degree of similarity of the first watermark vector with the comparison watermark vector; and using the degree of similarity to determine a relationship between the first watermark vector and the second watermark vector, the determined relationship not being based on whether the degree of similarity indicates a match between the first watermark vector and the comparison watermark vector; wherein the step of extracting a first watermark vector includes synchronizing at least the portion of the first digital representation with the portion of the second digital representation, wherein the second digital representation includes synchronization marks that are locatable in the second digital representation using a secret key, wherein the secret key is used to locate the synchronization marks in the first digital representation which are used to synchronize at least the portion of the first digital representation. - View Dependent Claims (2, 3, 4, 5, 6)
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7. 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 second watermark vector belonging to a second watermark embedded therein and the method comprising the steps of:
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an apparatus performing the following; 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 second watermark vector is embedded; obtaining a comparison watermark vector that is a replica of the second watermark vector; computing a degree of similarity of the first watermark vector with the comparison watermark vector; using the degree of similarity to determine a relationship between the first watermark vector and the second watermark vector, the determined relationship, not being based on whether the degree of similarity indicates a match between the first watermark vector and the comparison watermark vector; wherein the second digital representation includes synchronization marks that are locatable by summing information in a subsequence of the sequence of images, and the step of synchronizing at least the portion includes summing the information in the subsequence to locate the synchronization marks in the first digital representation, and using the synchronization marks in the first digital representation to synchronize at least the portion of the first digital representation, and wherein the information to be summed is locatable using a secret key, and the step of synchronizing includes the step of using the secret key to locate the information to be summed.
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8. 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 second watermark vector belonging to a second watermark embedded therein and the method comprising the steps of:
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an apparatus performing the following; 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 second watermark vector is embedded; obtaining a comparison watermark vector that is a replica of the second watermark vector; computing a degree of similarity of the first watermark vector with the comparison watermark vector; and using the degree of similarity to determine a relationship between the first watermark vector and the second watermark vector, the determined relationship, not being based on whether the degree of similarity indicates a match between the first watermark vector and the comparison watermark vector; wherein the step of obtaining the comparison watermark vector comprises obtaining information from which the comparison watermark vector may be computed, and computing the comparison watermark vector from the information, wherein the information from which the comparison watermark vector may be computed includes a message, the message being represented by the second watermark vector and the message determining at least in part locations at which the second watermark vector is embedded in the second digital representation. - View Dependent Claims (9, 10, 11)
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Specification