What I did was upload my photos to a hosting site (I used Photobucket) then copied-and-pasted the IMG code into the reply box.
With Photobucket, it gives your three different options to copy for each picture. One is the standard URL, one is the HTML code, and one is the UBB style IMG code. You'll want to use the latter. It's just a matter of highlighting the code under the picture you want, and copying (either rightclick and select copy or hit CTRL+C) then go to the reply box and hit CTRL+V to paste it.
The code should show the url surrounded by IMG tags, which are [ IMG] and [/ IMG] (but without a space between the [ and IMG parts).
Lemme know if you need anymore help.