What artwork has been copied more times than any other? It is modern. Remember, it could be anywhere, on any everyday object to qualify as a reproduction. E.g., all the posters, t-shirts, &c of Che Guevara would count, but that's not the winner.
Accoding to the Telegraph, it is this image of Queen Elizabeth 2 which has appeared on 320 billion stamps:
My question; is that US billions (a thousand millions) or UK billions (a million millions = US trillion)?