1. A spam fax filter comprising: a fax transformation processor configured to transform rasterized fax images into non-rasterized representations of fax images; a knowledge base of fax characteristics comprising at least one fax characteristic selected from the group consisting of spam characteristics and non-spam characteristics; and, a comparator configured to compare non-rasterized representations of fax images produced by said fax transformation processor with at least one of said fax characteristics to detect spam fax in the spam fax filter.