I was hoping someone else would answer, as I am not familiar with the best way.
One way would be to host the image with some sort of free online photo hosting service, and then post the URL here. You might even try leaving the "Enable formatted text" checkbox checked, and typing something like:
where www.whatever.com is the url to the image. (I haven't tested it, but it should work.)
There might be a better way, but I don't know it. Some of the others post images routinely...