Chaos based spread spectrum watermarking algorithm

This paper presents a blind spread spectrum watermarking algorithm in discret cosine transform (DCT) domain based on chaotic sequence features for still image. We used logistic map with two secret keys; one to generate a spread spectrum sequence and other to determinate the secret insertion positions of the mark; the insertion of the mark was done in the middle frequency of DCT of the image to be watermarked. This allowed to have a compromise between invisibility and robustness against scaling, rotation and cropping attacks.