In this paper, we propose a DCT-based blind watermarking scheme based on spread spectrum communications. We compute the DCT of non overlapping 8x8 blocks of the host image. Then using the DC coefficients of each block we construct a low-resolution approximation image. We apply block based DCT on this approximation image, then a pseudo random noise sequence is added into its high frequencies. For detection, we extract the approximation image from the watermarked image, then the same pseudo random noise sequence is generated, and its correlation is computed with high frequencies of the watermarked approximation image. We evaluated the robustness of the proposed technique against many common attacks such as JPEG compression, additive Gaussian noise and median filter. Compared with related works, it proved to be highly resistant in cases of compression and additive noise, while preserving high PSNR for the watermarked images.

Keywords