[Image theft htaccess and online aggregators from Ben Hammersley’s Dangerous Precedent][1]

How about since you’re already using mod_rewrite, add a section that says, oh something like this:

RewriteCond %{HTTP_USER_AGENT} !^Bloglines.* [OR]

RewriteCond %{HTTP_USER_AGENT} !^NetNewsWire.* [OR]

RewriteCond %{HTTP_USER_AGENT} !^AnyDesiredAggregator.*

RewriteCond %[HTTP_REFERER} !http://.*benhammersly.com

RewriteRule .*.(gif|GIF|jpg|JPG)$ http://benhammersly.com/images/pleasedontstealmybandwidth.gif [R,L]

[1]: http://www.benhammersley.com/weblog/2004/06/20/image_theft_htaccess_and_online_aggregators.html