1. An image processing method comprising the steps of: detecting the statistical distribution of permutations of pixel properties amongst contiguous groups of a predetermined number of pixels in at least a portion of an image under test, so as to derive feature data in respect of at least that portion of the image under test; and comparing the feature data derived in respect of the image under test with feature data derived from at least respective portions of one or more other images so as to detect a degree of similarity between the image under test and the one or more other images.