Based on some important properties of chaos, such as ergodicity, quasi-randomness, and high sensitivity to the secret key, chaos is a hot research field in secured communication, and recently a variety of chaos-based cryptosystems have been proposed for achieving the confidentiality of transmitted images over public channels. Most of chaos-based encryption algorithms are based on the Fridrich structure, which use separate confusiondiffusion layers. In this paper, we give an overview of some chaos-based block cryptosystems, including our cryptosystem, using dependent diffusion, in which the confusion process and diffusion process are performed sequentially on each pixel of the plain plain image. This kind of cryptosystems are more efficient than the traditional confusion-diffusion architecture of Shannon. A comparison study of efficiency in terms of speed performance and of robustness against cryptanalysis is done.