sweet, so now there will be even more red X's on the site!!!
a lot of site's don't allow hotlinking. Especially the one's with 'joke pictures' etc. However the pic will usually show up for the person who posts it due to it already being in their cache so they won't notice, but everyone else will get a red X (or nothing in FF).
Not to mention that a lot of images are indirectly displayed through a script (such as most forums including ours), so even if they do allow remote linking it won't show up because the script usualy won't execute unless it originates from the same domain.
Some people may know what will & won't work for remote linking, but chances are those people don't need instructions on how to do it.
I know you're trying to reduce disk space and bandwidth, but there's more efficient way to do it than this
Maybe there is a forum hack out there that will apply a quota to images that people upload in certain forums (jokes, around the bonfire, etc), but let others go unlimited (ie no limit to pics posted in events debriefing, carnage, etc). Or install one of those image optimizers we talked about waaay back when