I think everyone would want to know if their image was stolen unless they specifically said it was a give away. How about a checkbox on upload where the artist can select one of three options.. 1. Copyright protected, do not use for any purpose. 2. Private use for desktop and personal screensavers ok, all other uses reserved by copyright. 3. Public domain, do as you like. That way the folks who really want a pic may find several public domain images to chose from. Maybe if there is a public domain genre?