Multiple Watermarking Using Gram - Schmidt Orthogonal Processing

In this paper, we consider a multiple watermarking for image copyright protection. Multiple watermarking can be defined that two or more watermarks are inserted into the same content. Multiple watermarking using spread spectrum technique is able to extract the correct watermarks from the watermarked content when the orthogonality among keys should be guaranteed only. To keep the orthogonal property between keys, we perform the process of Gram-Schmidt on the random sequences. The orthogonalized sequences are used as keys to embed the watermarks. The proposed method can not only extract correctly the embedded watermarks but also show the robustness against various attacks such as Gaussian noise addition, histogram equalization, gamma correlation, sharpening and brightness/contrast adjustment.