So far digital watermarking has been indicated as the most feasible answer for multimedia copyright protection issues, though many problems, especially regarding aspects of robustness against geometrical attacks, have not been completely and adequately solved yet. Robustness against geometric manipulations has been dealt with by inserting, together with the watermark, a synchronization template to be used later in the detection phase, to determine if a geometric distortion occurred and invert it before looking for the mark. A novel technique is presented, which, by exploiting the theory of geometric invariants, inserts a watermark intrinsically resistant to this sort of manipulations, thus avoiding the need of a synchronization pattern. Preliminary experimental results proving the goodness of the methodology are discussed along with some implementation problems due to the computational complexity.
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