Cryptanalysis of correlation-based watermarking schemes using single watermarked copy

Most of the existing digital watermarking techniques are based on correlation between "some information stored in the watermarked copy" and "related information retrieved from attacked watermarked copy". We show how to remove this correlation to mount a ciphertext-only cryptanalytic attack on these watermarking schemes. The attack needs only a single watermarked copy of the image. Our work clearly raises question on the basic watermarking paradigm based on correlation measures.