Method and apparatus for discerning image distortion by reference to encoded marker signals
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United States of America Patent
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May 20, 2003
Issued Date -
N/A
app pub date -
Apr 27, 2000
filing date -
Nov 18, 1993
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
To permit scaling or rotation of an image to be discerned--even if the original image is not available--certain marker signals are steganographically encoded in the image. In one particular implementation, encoding is effected by adding an overlay signal to the image. The overlay signal--when represented in the spatial frequency domain--includes a pattern of spots. If the image is scaled or rotated, this pattern changes in known ways. By examining the change in this pattern, the distortion (i.e., scale/rotation) of the image can be inferred. This technology finds particular application in conjunction with watermarking systems, permitting recovery of watermark data from images that have been scaled or rotated subsequent to watermarking.
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