A lithophane depicting Saul Goodman. It becomes a very high-detail image once you shine a light behind it, whether it's your ceiling lamp or you've put it on an outside-facing window (during the daytime, at least). 

Everyone loves Saul!

This works best with white filament, I wouldn't print it in any other color. It is printed in 0.1mm layer height for maximum image fidelity. 

Also, sorry if the posted image sucks. Had to take it from a video.