1. A method of representing a group of images, the method comprising determining the values of one or more dominant colours for the group of images and deriving a dominant colour representation expressing the group of images in terms of one or more of said dominant colour values, wherein at least some of the images in the group of images are represented by a respective dominant colour representation in terms of one or more dominant colour values for the image, where each of the dominant colour representations has one or more components including at least one dominant colour value, and optionally for each dominant colour value, a variance indicating colour distribution variance of the image with respect to the dominant colour value, a weight indicating the influence of the dominant colour in the image, the number of dominant colours in the image, and spatial homogeneity of pixels corresponding to the dominant colors in the image, the method comprising combining a plurality of said dominant colour representations or selecting one of the dominant colour representations as representative of the group, comprising combining, in a first stage, components for which the distance between the respective dominant colours satisfies a predetermined condition such as being less than a predetermined threshold, and combining other components in a second stage.