A friend of mine has a problem with his images getting linked by bulletin board groupies looking for cool avatar images. Rather than provide their own bandwidth, they deep-link into his site and use his bandwidth. Punks!
He now has his web server restrict images from being served unless they’re referred to from a local page, but I never knew how to set it up. I just happened to come across the how-to here. The .htaccess changes look like:
SetEnvIfNoCase Referer "^http://my.host.com/" local_ref=1 <filesMatch ".(gif|jpg)"> Order Allow,Deny Allow from env=local_ref </filesMatch>
Haven’t tried it myself yet, but made a note.