I like this thread too, so I hope your efforts succeed.
Here is a mystery picture" that I bought at a magic and joke store when I was probably ten or eleven (1952 or so).
I looked at it every time I went there and couldn't figure it out. As with the 'magic' tricks and other goodies, you had to buy them before the owner would tell how they worked.
Damn, but that place was hard on my allowance.
I still have that postcard and it still stumps people.
Of course once you know what it is, you can't look at it without seeing it, so I can't say if it is going to be hard or easy here.
I found it online with my first Google try.
http://www.optical-illusionist.com/i...s/mystery1.jpg