I had a problem where someone linked to one of the images on this site (actually problem still exists), basically a 2mb+ image was being displayed on some forum (I won't include the link :-))  which used a huge amount of my bandwidth... Well, here's a solution, also a pretty nice display of using HttpModules...he also has some nice, hi-res wallpaper here (wouldn't try to deep-link them though :-P)