A robust spread spectrum watermarking method using two levels DCT

Abstract

In this paper, a discrete cosine transform (DCT) based blind watermarking scheme based on spread spectrum communications is proposed. We perform block-based DCT (BDCT) on the host image; then using the DC coefficients of each block, we construct a low-resolution approximation image. We apply BDCT on this approximation image, then watermark is embedded by adding a pseudo random noise sequence into its high frequencies. In detection stage, 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. In our method, higher robustness is obtained because of embedding the watermark in low frequencies. In addition, higher imperceptibility is gained by scattering the watermark's bit in different blocks. Compared with related works, our method proved to be highly resistant in cases of many common attacks, while preserving high peak signal to noise ratio for the watermarked images.