1. A method for identifying a region of interest (ROI) in an object from a set of similar images of different instances of a said object, said method comprising: using a suitably programmed computer to compute a weighted map of a feature of said image in which the weight of said feature at each location in said map is calculated to minimise the sample size needed to distinguish a first group of said examples from a second said group, said ROI consisting of the set of locations in said map at which said feature has the highest weights.