I don't know if there are other ways to do this, but this is how I post pictures on the forum.  

First: Post the picture to an image sharing website such as:
http://imgur.com/  http://photobucket.com/  Next: Right click the image and select the option 
 "Copy Image URL"Finally: Paste the image url so it looks like this 
[ img ] URL goes here [ /img ](an easy way to do that is on the toolbar of the reply box there are options underneath the "bold", "italics", and "underline" options... you want the option that has a picture on it. It will automatically paste the code in the reply text box.) 
Hope this helps ^.^
~imp
PS. If you have other ways of doing this or have any questions... post a reply! ^.^