Maureen -
You can either reference a photo on another web site, or you can upload a small image. To upload a small image, look below the box where you are typing your message. Under Additional Options, there is a button that says Manage Attachments. You can use that to point to an image on your computer that is then uploaded to the site.
The problem is that images that are uploaded in this fashion are limited in size - so it's very possible that your photo is larger than is allowed there. Photos can be resized, but you will need a tool on your computer to do that.
--- Denise