1. An image retrieval system comprising: a database with candidate images; entry means for entering a query image; first histogram means for deriving a first query color histogram from the query image; second histogram means for deriving a first candidate color histogram from a selected candidate image; determining means for determining a first similarity between the selected candidate image and the query image on the basis of either: i) a Kullback informational divergence between the first candidate color histogram and the first query color histogram; or ii) the entropy of the distribution of similarity coefficients over bins of the first candidate color histogram and bins of the first query color histogram; and retrieval means for retrieval of the selected candidate image, selection thereof being determined by the determining means on the basis of information conveyed by the first candidate color histogram in response to information requested by the first query color histogram.