1. A method of creating a shape descriptor representing an object appearing in an image or sequence of images, by processing signals corresponding to the image or images using one or more processors, the method comprising deriving, using a processor, a curvature scale space (CSS) representation of the outline of the object by smoothing the outline of the object; deriving, using a processor, an additional parameter reflecting the shape or mass distribution of a smoothed version of the original outline of the object; and associating the CSS representation and said additional parameter as a shape descriptor of the object, wherein said additional parameter corresponds to a circularity of a smoothed version of the original outline of the object.