1. A method of representing an object appearing in an image or a sequence of images, by processing signals corresponding to the image or images, the method comprising: deriving a curvature scale space (CSS) representation of an outline of an object starting from an arbitrary point on the outline, by smoothing the outline in a plurality of stages using a smoothing parameter, resulting in a plurality of outline curves; using values for points of inflection of each outline curve to derive characteristic curves which are characteristic of the original outline; selecting first co-ordinates of peaks of said characteristic curves, which correspond to the smoothing parameter, and corresponding second co-ordinate values representing the positions on the outline corresponding to the peaks; and shifting one of the second co-ordinate values to zero, and shifting all the remaining second co-ordinate values corresponding to said peaks by an amount equivalent to the original co-ordinate value of the second co-ordinate value shifted to zero.