This fraud method uses an "" HTML tag where the "src=" image source parameter is set pointing to the Click-tracking URL, instead of pointing to a real image file on the server. The request will recieve a cookie from the tracking server, instead of an image, hence no image displayed. The browser stores the cookie on client computer. Subsequently, when the visitor makes a purchase at the advertisers e-commerce site, the cookie will identify the rogue affiliate as the source of the traffic, and the rogue affiliate will recieve the commission.
It is usefule for the tracking software to examine the "Referrer" field in the header, to ascertain the source of the click.