That showed up as a red box with an x in it.
Greebo: What you use is the URL= bbcode tag, and inside the target you use the IMG tag, then close the /URL tag after the image.
Hotlink, subject, close hotlink.
EDIT: Okay, I'll use () instead of [].
(URL=http://etc.blah.com/img1.jpg)(IMG)http://etc.blah.com/img1_thumb.jpg(/IMG)(/URL)