I suppose this is a dynamic image. The server grabs your IP address, writes the text into an image and serves that image. Still wouldn't get you a TOR user's real IP address.
The thing that freaked me out was that I misunderstood OpenYourEyes' post to mean he could embed arbitrary flash or java code into a simple HTML forum post AND make it execute on the victim's computer automatically and so, through these systems' bypassing of proxy settings, learn joe23's real IP. This would be a very serious security flaw, I expect.
Can anyone suggest a web page where the privacy of your web browser is tested? Like one that tries java, js, flash, html, php, other bug exploits to track an IP, even behind tor?  I know panopticlick from the EFF. Anything else?