A computer implemented method for predicting preferences of an observer for two images, the method comprising the steps of: receiving the first image and an associated salience map indicating regions of the first image that are likely to be scrutinized by the observer; receiving a content masking map indicating differences between the first image and the second image that the observer is likely to be able to perceive; determining a number of preference measures; and processing the salience map and the content masking map to determine a distribution of a set of values of the preference measures predicting the preferences of the observer for the first image and the second image, the set of values of the preference measures having a number of degrees of freedom.