A spread spectrum watermarking scheme based on periodic clock changes for digital images

This paper proposes a spread spectrum watermarking scheme based on periodic clock changes (PCC) for digital images. The PCC spreading properties and applications in multiuser communications are recalled. This alternative spread spectrum technique is compared with a classical Direct Sequence (DS) method in terms of robustness to attacks and noise, secret message bit rate and multiple watermarking performance. PCC proves to be a simple alternative to pseudo-noise modulation spreading methods, that provides similar performance.