I would say the solution will have to depend on exactly how the images are used. If they are always taken out of context and no credit to you is given whatsoever, you may want to prevent showing hotlinked images. However, although I think this is the most common way hotlinked images are used, it's not the only way. I'm involved in an interesting circle of blogging activity where people *profusely* hotlink everyone else's images and yet at least "some" credit is usually given, although mostly not an actual html link that I would have liked.
I toyed with an idea of replacing the hotlinked images with the thumbnail versions of them and a note (text embedded into the replacement image) saying "to see the full size image go to http://www.example.com/page1.html" but then discarded it because it's very intensive CPU-load wise (although caching can help tremendously) but also because it will make me look like a jerk in the blogging circle which I respect despite all the misgivings. In other words, a "Stop Theft" replacement image solution (or even a softer version of it) would most likely backfire for me and instead I just grumble and watch my bandwidth being wasted (fortunately it's free these days though server load isn't)