A robust digital watermark procedure for still images using DCT phase modulation

A digital watermark is a short sequence of information containing an owner identity or copyright information embedded in a way that is difficult to erase. We present a new oblivious digital watermarking method for copyright protection of still images. The technique is based on modifying the sign of a subset of low frequency DCT magnitude coefficients. The embedding process is adaptive and maintains a compromise between robustness and imperceptibility. A major advantage of the technique is its complete suppression of the noise due to the host image. The robustness of the technique to a number of standard image processing attacks is demonstrated using the criteria of the latest StirMark benchmark test.