What are the most recognized art history images?

Mona Lisa

But, from the perspective of images most often encountered (in the generic sense) in art history courses, my recollection suggests that fertility images have been recognizably most prominent across all eras and cultures, a prime example of which would be the Mona Lisa.

Second to that, if not first before that, I would guess to be phallic symbol images; of course, one might argue that a phallic symbol is also a fertility symbol--and the Egyptains, for one, seemed to have no reservations about the both-sides view of procreation in art imagery.