Phil Craven sets the record straight on images not having PageRank at this Search Engine Watch thread. Basically, if you link directly to an image source, such as yahoo-unicode-arrows.gif, PageRank should not pass to it. However, if that image is a Web page, like linking to a page like this because it has a cool image of a dog, even cooler in 4 colors, it will pass PageRank.
So I just ripped off that image from that site, actually I really downgraded the quality of the image, because I felt bad. But people rip off images from sites all the time. Mikkel, in that thread recommends using a "rewrite rule (if you are on Apache) that check if the image is requested from within our outside your domain (external request)." Then serve up a different image, of something ugly as a game.