This is fun and cool. You can now order custom photo stamps on Stamps.com. This is apparently legitimate US postage, customized with your images. Very slick.
On a side note, I met with these guys a long time ago when I was doing Works. They were interested in some kind of integration so we could print postage on envelopes directly, as I recall. Nothing ever came of it, but I recall being impressed with the people, but wondering if they'd make it. I guess they're still around, so good for them.