Abstract: In this paper, the authors summarized the latest development of the image encryption techniques. Some techniques such as (1) matrix transform/pixel permutation based, (2) pseudo-random sequences based, (3) SCAN language based, (4) "secret key image" based, (5) SCAN language with quadtree coding based, and (6) commercial cryptography with vector quantization coding based image encryption techniques were illustrated. Advantages and disadvantages of these algorithms were compared and the suitability was discussed respectively. Particularly, the chaotic image encryption technique was presented;some advantages with chaotic technique were illustrated and some valuable problems were pointed out for further research.