Summary form only given. Image data compression by fractal techniques has been widely investigated. Although its high compression ratio and resolution-free decoding properties are attractive, the encoding process is computationally demanding in order to achieve an optimal compression. This article proposes a fast fractal-based encoding algorithm (ACC) by using the intensity changes of neighboring pixels to search for a suboptimal domain block for a given range block. Experimental results show that our algorithm achieves close to the optimal algorithm (OPT) for 256/spl times/256 images Jet, Lenna, Mandrill, and Peppers, with a compression ratio of 16. A comparison of the performance of algorithms OPT and ACC on a Sun Ultra 1 Sparc workstation is given.