A spam fax filter which has been configured in accordance with the present invention can include a fax transformation processor configured to transform rasterized fax images into non-rasterized representations of fax images. The spam fax filter further can include a knowledge base of known spam characteristics. Finally, the spam fax filter can include a comparator configured to compare non-rasterized representations of fax images produced by the fax transformation processor to the characteristics in the knowledge base to detect spam fax in the spam fax filter.