Did you know X-ray technology is currently allowing art historians to peer underneath famous works of art and see what might be hidden underneath? We may one day discover that Leonardo da Vinci first painted Mona Lisa as a bad ass pirate or perhaps a stealthy ninja assassin. No need to wait for that almost certain eventuality!
-Original Mona Lisa!
-Pirate Mona Lisa (with eyepatch and flintlock pistol)
-Ninja Mona Lisa (with katana and throwing star)
These are perfect for etching into wood and other materials that will give you proper contrast. Whiteboard works best from my experience.
I suppose you could also create some kind of Mona Lisa ninja/pirate hybrid but I'm not responsible for what might happen to you...