Apparatus and an accompanying method for an iterative convolution filter for determining an image signature and which is particularly useful in a system for automatically classifying individual images, on a numerical basis, in, e.g., an image database, and, through a query-by-example paradigm, retrieving a desired image(s) therefrom. Specifically, a signature is computed for an image using multi-level (e.g. L levels) iterative convolution filtering, with pixel values for each color axis supplied as input to each filtering level being separately convolved with each one of a set of, e.g., K predefined kernels, each being, e.g., a derivative of a Guassian kernel, to yield an output image. Each of the output images, of which K.sup.L occur for each color axis, is either applied as input to the next filtering level or applied to a summer to yield a resultant sum over all pixel values in that particular output image. This sum becomes the value of a corresponding one of K.sup.L elements, for each color axis, in the signature.