Leonardo Da Vinci was a Friggin Genius
Leonardo Da Vinci allegedly painted his initials and those of his sitter for the Mona Lisa into the eyes of the painting. Zooming in using a camera shows initials painted in thin black letters on top of the dark green and brown of her eyes. Leo used a very thin brush and a magnifying glass to do so and this small detail went unnoticed for hundreds of years. Fortunately for him everyone liked his painting and we kept it around until we had the technology to see this subtlest of details.