Dated to circa 200 AD, the Alexamanos graffito from Rome is the earliest depiction of Jesus and his crucifixion. It reads "Alexamanos worships his God" and shows an image of a man raising his hand to a crucified man with the head of a donkey, obviously intended to mock.
At the time, Christians were accused of worshipping donkeys.
A second interpretation puts the figure as being Anubis or Seth, but this seems less likely.
In another hand nearby reads "Alexamenos fidelis" - Alexamenos is faithful.