lucy24 - 9:24 pm on Mar 4, 2012 (gmt 0)

Funny you should ask that...

# unconditional
RewriteCond %{HTTP_USER_AGENT} facebookexternalhit [NC]
RewriteRule \.(jpe?g|gif|png)$ - [F]

Everyone else gets the "no hotlinks" image, but these folks get nothing. Nothing, d'you hear? Nothing, nada, nil, no hotlink-facilitators wanted. Someone hereabouts once explained what it looks like from the FB member side. All I know is, you have to nip them in the bud before it gets to the hotlink stage.