Caravaggio's Head of Christ from the Calling of Matthew
Yes, I know! I flipped it. I have my reasons. . . funny thing is, after I flipped it, I read that Caravaggio was known for working with mirrors! So this may actually be closer to the original pose. This is a detail of his painting. Here is the whole painting, not flipped:
This is how my copy of Caravaggio's Head of Christ from the Calling of Matthew started. Click the image above for an explanation.