I've been suggesting the server-side screenshot thing for as long as I can remember. As far as I can tell, its the only way to be sure whether or not someone is wallhacking. For the competitive DP scene, wallhacking is the only problem, right? Aimbots are easy to detect just by camming someone, but wallhacking is a little harder, depending on how well they hide it or not.
Maybe we should start talking about making a standalone .exe that you enable before you enter a match, and randomly during the match it takes screenshots of your computer, not just dp. Then after the match it uploads the screenshots to a free image service like imageshack, maybe even flickr. Infact, with flickr you could use the developer api and make the images available to the public.