Hi Kevin - you'll need to host your image on another site and link from your post (the AC3D site doesn't allow for local storage of images). Once you have the URL for the image, just use the "img" tag in the post editor.
You could try
http://photobucket.com/ if you need a place to land images --- more of a suggestion than an endorsement, as I haven't used it myself, but it seems fairly popular...