To add a photo you have to first upload it on line somewhere else (facebook, picasa, etc and then obtain the url that corresponds to it. From there, when you're entering text into the comment-entry box, place an image tag like you would if you were building a web page. Of course if you've never built a web page that's absolutely no help.
Place a "<" first, then put "img scr=" then put the url for the photo and finish with the ">".
I hope that helps.
Good luck.