This is how I found it:
I have a program I use to tag 1 or few pics from each one of my folders.
I use to run this program to view some thousands of pics according to those tags.
I have the pic I posted tagged in that program and each time I run the program I see always the same pics.
If one of those pics became a puzzle, I recognize it at once and with a quick search in my HD I find it back.