you can post a gif but it wont play you have to click
say you want to post this pic http://farm1.static.flickr.com/173/378089386_79171b7c90.jpg . I kept getting fucked up because i would put the " [img]'s" in after pasting the url.
try typing [img]PASTE COPIED URL(then, without moving the cursor type [/img] ) . This is probably what you are already doing, but that's where i got all turned around.