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Geometric attacks are among the most challenging problems in present day data hiding. Such attacks are very simple to implement yet they can defeat most of the existing data hiding algorithms without causing serious perceptual image distortion. In this research, we report a novel method to estimate the geometric manipulation. Geometric attacks can very easily confuse the decoder unless it transforms the image back to its original size/orientation, i.e., recover the lost synchronism. To be able do so, the decoder needs to know how the image has been manipulated, i.e., needs to know geometric transformation parameters. In our approach, the point pattern matching measure is computed for the geometric manipulation. The reference point patterns (i.e., a triple) are computed from feature ellipse of the original image. The point pattern matching is realized by genetic algorithm. The proposed scheme does not require the original image because reference triple information of the watermarked image has been contained in the secret key. Novel method has been proved its robustness to geometric attacks through experiments.

Keywords: digital watermark, reference points extraction, points matching, genetic algorithm, robustness

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Received April 16, 2005; revised June 24, 2005; accepted June 30, 2005.
Communicated by H. Y. Mark Liao.