Until a guide is set up, the most straightforward and easy way I know of is to host an image on Flickr or Photobucket, get the image url, and use the image brackets.
Example (delete spaces when using this in a real post):
[ img ]http://static.flickr.com/79/209226842_be3bb1b9f5.jpg[ /img ]
If you post that directly without spaces, you'd get this:
Viola! Let us know if you have any other questions.
-Brad