You make $0 from the other sites hotlinking your images.
http://www.greenguysboard.com/board/...em#faq_hotlink was developed a few years back and still holds up pretty well.
Code:
RewriteEngine on
# leave this line in allow empty referrers, remove to disallow empty referrers
RewriteCond %{HTTP_REFERER} !^$ [NC]
RewriteCond %{HTTP_REFERER} !^http://(.*@)?([a-z0-9-]+\.)?yourdomain\.com(:[0-9]+)?(/.*)?$ [NC]
RewriteCond %{HTTP_REFERER} !^http://(.*@)?1\.2\.3\.4(:[0-9]+)?(/.*)?$
RewriteRule .*\.(asf|mpg|mpeg|wmv|avi|rm|gif|jpeg|jpg|zip)$ - [NC,F,L]
The 1.2.3.4 should be replaced with your IP address if you want -- or, you can remove that line entirely. Nowadays, it probably doesn't matter much to have that line there. Allowing the Empty referrer is probably good because a lot of privacy software tends to blank the referrer line. However, if you are being heavily hotlinked, you might disable that since some of the forum surfers won't be sending referrers specifically because they know most rules will allow the image to be hotlinked with referrers turned off.