1. A method of detecting spam images in electronic objects, the method comprising: extracting images embedded in the electronic objects; compressing the extracted images into a common representation using a lossy compression function; determining if the compressed forms of the extracted images are identical to the compressed form of any known spam image from a corpus of known spam images, which compressed forms are the known spam images compressed into said common representation using said lossy compression function; and signalling electronic objects as embedding a spam image on the basis of a compressed form of an extracted image extracted from an electronic object being determined to be identical to the compressed form of a known spam image.