For the shortcoming that transform domain watermarking cannot resist image rotation attack, this study draws LPT (Log-Polar-Transform) theory into watermarking field, then puts forward a new improved algorithm based on LPT and DFT. Before embedding watermarking, first do LPT and DFT of the carrier image, because LPT and DFT theories respectively have good scale invariability and synchronicity when image rotation happens, they can provide an environment with an ability of resisting rotation; then spread the watermarking information spectrum with a pseudorandom sequence. In the end, embed the sequence into the low frequency band of the carrier to complete the embedding part. In process of detecting, rotate different angles of the carrier and extract the watermarking, calculate the correlation value between extracted watermarking image and carrier image. The experimental result proved that the algorithm could manifest a good robustness when it was attacked by image rotation and some other image attacking methods.
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