Rate distortion optimization for efficient watermarking in the DCT domain

In this work we concentrate on a unique algorithm for watermarking, which is based on a modulo operation method. This method hides an integer number in the sum of the quantized DCT coefficients in a JPEG block. We use the Lagrangian optimization algorithm, which enables us to select the possible coefficients that will be changed in order to insert the watermark while controlling the bit rate and the distortion level (MSE). The uniqueness of this work is that by integrating the rate-distortion optimization method with the watermarking process we can control the rate of the watermarked image with minimum additional distortion. Initial results of our algorithm show that we can add 4-5 bits per DCT block (8times8 pixels), with a distortion level of 0.7 [dB] at JPEG compression quality above 75%.