Did you solve it? Bongard picture puzzles that will bongo with your brain.
Marlene Breverman stashed this in Puzzle-ing
The challenge with Bongard problems is to find the rule that applies to the six left-hand images, and the rule that applies to the six right hand ones, which is often the negation of the left hand rule.
All the rules are easy to explain - but even so it is extraordinarily difficult to find them.