When posting a new message, there is a bunch of icons above the text field. The fourth one in on the second row (looks sort of like a picture) adds in the command you want.
You can also do it manually by enclosing the address of the picture in [img] tags like so:
[img]http://www.SITE.com/ADDRESS[img]
The ending [img] tag has to have a / before the "i" in "img'. I can't write it or the software will think I'm inserting an image and you won't see most of this text.
Now, if you don't have a website you can upload it too, email the picture to me at chrios@rocketmail.com, and I'll upload it here. Then you can use the address:
http://www.slinging.org/images/YOURPIC.jpgChris