I remember a guy (call him "Joe") who had a website with lots of nice images on it. Forum people often added one of Joe's images to their sig lines via a link to the image on Joe's site. So, anytime anyone read a post they made, Joe's server would have to serve up that pic in their sig line, using up Joe's bandwidth. Joe's site was plastered with messages about the legalities, and pleaded with people to stop stealing his bandwidth.
Eventually, Joe fought back. When his statistics showed a particular image was being downloaded a lot, he'd follow the links out and discover the mis-use. Then he would replace the image on his site with a gay porn image.
For a time on the forum, scrolling thru a thread you'd see images flicking by something like: Chevy 1500, Chevy logo, Chevy 1500, Chevy 2500, Monster truck, Chevy logo, GIANT PHALLUS, Chevy 1500 etc, GIANT PHALLUS, then a bunch of "WTF??!!" posts about the giant phallus... Trust me, it's for more jarring to see than to read about it.
Hilarity ensued. Eventually I think people got the point, but interestingly, they were usually mad at Joe. Kind of like suing someone for getting hurt in their house while robbing it.