You need to host the picture on a separate site like photobucket, tinypic etc. and place the image URL between the "s. The img src tag doesn't have and ending tag like the other ones, and there seems to be a typo in the tag list on the right when you write/reply to a post so I see why it could be confusing.
Web Browsers have a Quirky Mode or Compatibility Mode that they go into when they detect missing or improper coding. When the browser goes into this mode it will correct the errors like properly closing the tags for you but sometimes the browser will not close the tags right causing a render error. So a Mikel put above it is proper to close those tags out so you do not force the browser to do it wherein it can cause errors.
I'm not going to be a jerk and say that technically I was right, perhaps a better piece of information is this; I learned HTML from a huge book I bought a long time ago regarding HTML 1.0 or something like that. XHTML is a term I have yet to look into :)
Though I'd like to end this rather pointless argument of ours with the following observations;
- When you click reply and get the list of available bbCodes you can use, it specifically states HTML ON.
- OP was talking about HTML, not XHTML.
- Assuming people will view source code to understand how forum features work, on their own, when relatively straight forward game mechanics that are elaborated upon in the rules gets numerous threads in the help section during a year, is a wee bit far fetched.
Technically you were right, assuming everyone involved understood that we were talking about XHTML. There's a reason I used the wording "...it seems", and that is because I don't keep myself up to speed on the latest developments :)