In this paper, we present a new approach for encrypting binary images. Putting different scan patterns at the same level in Ž .the scan tree structure and employing a two-dimensional run-encoding 2DRE technique, our encryption method can encrypt images with higher security and good compression ratio when compared to the previous results. Detailed security analysis from the combinatorial viewpoint is also given. Some experimentations are carried out to illustrate the good performance of our proposed method. q 1998 Elsevier Science B.V. All rights reserved.