Where is the image located? I don't think you can attach pictures like other forums, so you need to have the picture hosted somewhere. My pictures are hosted on Webshots, but you can also do them here on Audiocircle, just create a Gallery, its one of the links up top.
If you go the Webshots route there is a link on the picture for posting on forums, you just copy paste the address in and viola, pic. If you want to see the HTML you can click the quote button on my post with the pics to see it.
If you go the Gallery route then once you have the pictures in their right click on them and go to properties, and copy the url. Then click on the image insert button, and paste the url in, and the pic should be in there. Just make sure it doesn't say small at the end of the pic, if so you got the thumbnail and the pic will come out small.