All I do is copy the link from the image I want and then in the reply area press the IMG button and paste all the info into that.
Below is the code I used but you'll notice that the brackets are reversed so the word IMG is encased by ][ instead of [] like it should be. Not really sure if I'm explaining it well enough but I hop this helps some.
]IMG[
http://www.emuasylum.com/images/logo.jpg]/IMG["