Theory and method in digital communication have been applied effectively to the embedding and detection of digital watermark. The method is efficient to embed the watermark bits into the digital media by the principle of CDMA communication due to its many advantage

such as

multiple-accessing

excellent secrecy

standing firmly against disturbing

and resisting noise attacks etc. In this paper

a DWT-based image watermarking algorithm applying DS-CDMA is proposed. The orthogonal Gold sequences sets generated via the preferred-pair of m sequences are well improved

and then are used to spread spectrum of the watermark. The CDMA encoded watermark is embedded into the DWT domain by modulating selected DWT coefficients of the image in a fashion similar to CDMA. Blind recovery of the embedded data is achieved by analyzing the DWT coefficients of the watermarked image and the auto-correlation of orthogonal codes. The proposed algorithm is compared with the existing watermarking schemes based on CDMA. The experiment results demonstrate that the watermark with the proposed algorithm is robust to JPEG compression

Gaussian noise and other typical attacks. The hidden information is secure well and hard to resist by unauthorized detection and attacks because of the same private key.