An image processing system has been developed around an APOLLO workstation, tailored to the needs of processing images of photo-elastic models. Using this system, the author has made a comparative study of image processing algorithms in the analysis of a disk of araldite resin loaded in diametral compression. A differential zero-crossing algorithm has been developed, and the results obtained are compared with those from the other algorithms. The algorithms used are described, and an analysis of their effectiveness in this problem is presented with the aid of a fringe analysis system developed to analyze output from the image processing system. The results are compared with those from a mathematical solution.