In 1980, while scheming a silver screen pitch, Michael Uslan, the man who bought the rights to “Batman,” came across a promotional image of Nicholson’s character from “The Shining” in the New York Post… Uslan painted over the image with whiteout and transformed Nicholson’s furious features into that of the clownish villain.

(Buzzfeed via artinfo)

And just for comparison, here’s (most likely) where Heath Ledger’s Joker came from:

(starts at the 1:30 mark)
vs.