A system for generating secure documents includes a station for generating a plain document and a security image generator that generates a security image. The security image is then incorporated into the plain document. Each security image consists of a plurality of secure elements, each secure element being defined by two sets of parallel lines. Each secure element defines an alphanumeric character or other unique image that is visible under certain conditions, i.e., when inspected through a viewer. The technique can also be used to provide security images on a web page as a means of indicating that the web page is genuine.