You can get packages of little girls' bracelets in various shapes pretty cheaply. I bought a butterfly one for about a dollar. You can use these to make crocheted frames!
All you have to do is work slightly loose single crochets around the shape, then continue to crochet to the size of frame you'd like. (As you can see, the points show on the butterfly, but that's okay. Obviously, a plain circle would be easiest!) I did some long single crochets between each section of the butterfly's wings to emphasize the shape.
For the back, just make a round piece big enough to cover the opening. Sew it in place a little more than halfway around.
Then you can just slip a picture down into it.
I'm linking to the Saturday Sparks link party over at "Pieced Pastimes." Go and check out what else is cool over there!