1. A method of processing a visual image, for identifying areas of visual attention, comprising the steps of: storing an image as an array of pixels, each pixel having a value; selecting test pixels from the array, for each test pixel, selecting one or more neighbour groups of pixels neighbouring the test pixel; selecting comparison pixels from the array; identifying a group of pixels neighbouring a selected comparison pixel having the same respective positional relationships to the comparison pixel as a selected neighbour group of pixels has to the test pixel; comparing the values of the selected neighbour group with the values of the identified group in accordance with a predetermined match criterion, and generating a measure of visual attention for each test pixel, in dependence upon the number of comparisons made for that test pixel for which the comparison results in a mismatch.