First, press the
Img* button - you'll get an
[img]on%20the%20screen.%20%20Paste%20the%20direct%20link%20to%20your%20images%20from%20imageshack/photbucket/etc.,%20then%20press%20the%20
Img*%20button%20again%20-%20this%20time,%20you'll%20see%20
[/img].
So in the message body, it'll look like this (I've intentionally deleted some letters and digits so the actual pic wouldn't post):
An easy way to look at it is to use the
Img* as quotation marks - you merely have to enclose the direct link of your images between them to post.
Remember though, you won't see the image in the message body as you're typing. However, you can press the "Preview" button at the bottom just to check if you've done it correctly.