Abstract: In this paper we propose, a blind digital image watermarking algorithm based on combined DWT-DCT transformation with low frequency watermarking. The watermark embedding is carried out by modifying the wavelets coefficients of carefully selected DWT sub-band of a host image after two levels of DWT decomposition, followed by the application of the block based DCT transform on the selected sub-band. Watermark embedding is done using low frequency coefficients of each selected 4×4 DCT block. The watermarked host image is exposed to several watermark attacks. Experimental results demonstrate that the proposed algorithm is able to withstand a variety of common signal processing and geometric attacks.

Keywords: Discrete Cosine Transform, Digital Image Watermarking, Discrete Wavelet Transform, PSNR.