Hello! I'm sure this has been done before but i was actually inspired by all the picture frames i've been making out of shells lately. I collected these rocks at a waterfall in northern Thailand where I live.
The finished project, complete with blind line dinosaur picture:

The making of:
Materials included: Elmer's glue, rocks, cardboard paper, scissors, and paint. (regular paper and pens for drawings)
1. cut shape of cardboard and glue on rocks, then cover with a coating of elmer's (this helps the rocks take the paint better and makes everything more secure.

2. Paint white

3. Paint blue

4. Add crystal shiny rocks (not sure what kind of rocks these little guys are, if anyone knows please share)

this one shows the shininess better

5. Add picture (first i did one of a waterfall, then switched to the dinosaur)

Thanks for looking!