Information theoretic bounds for data hiding in compressed images

We present an information-theoretic approach to obtain an estimate of the number of bits that can be hidden in still images, or, the capacity of the data-hiding channel. We show how addition of the message signal in a suitable transform domain rather than the spatial domain can significantly increase the channel capacity. We compare the capacities achievable with different decompositions like DCT, DFT, Hadamard, and subband transforms.