This is a Fan Art of the Joker from Alan's Moore Novel the Killing Joke. The original Artwork was Illustrated by Brian Bolland.
My approach to this piece was to mix the Stylized anatomical features of the Joker's original artwork and make a 3D photo realistic version of it, using tools like Substance painter and Marmoset Toolbag to achieve that photo-realism

More Pictures in my ArtStation post