Can you rename the folder your images are stored in once in awhile? It would mean you'd need to update your own links at the same time -- not so bad if you can do a global search-and-replace, but a pain otherwise.

Even better is if, in the location where your images used to be before you renamed the folder, you put new copies of your files with rude messages on them. That way whoever is trying to hotlink to your pretty pictures gets outed to their own site's visitors. I knew one graphics designer who used to call those "golden raspberries:" a way of saying "PBPBTHTHPH" to the bandwidth thieves. Emotionally satisfying, but it wouldn't stop the drain on your bandwidth.

So glad to hear your 'puter is better!