An oblivious robust digital watermark technique for still images using DCT phase modulation

Digital watermarking is the process of secretly embedding a short sequence of information inside a digital source without changing its perceptual quality. 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 robustness to a number of standard image processing attacks is demonstrated using the criteria of the latest Stirmark test.