  This paper investigates the multiplicative spread spectrum watermarking
method for the image. The information bit is spreaded into middle-frequency
Discrete Cosine Transform (DCT) coefficients of each block of an image using a
generated pseudo-random sequence. Unlike the conventional signal modeling, we
suppose that both signal and noise are distributed with Laplacian distribution
because the sample loss of digital media can be better modeled with this
distribution than the Gaussian one. We derive the optimum decoder for the
proposed embedding method thanks to the maximum likelihood decoding scheme. We
also analyze our watermarking system in the presence of noise and provide
analytical evaluations and several simulations. The results show that it has
the suitable performance and transparency required for watermarking
applications.
