I'd known about death masks for some time. I'd just forgotten about them until I read an article recently about them.
Death masks are real castings of a person's face (and sometimes hands or other body parts) soon after their death - for obvious reasons. In most cases the masks are of famous people, like the one of Benjamin Franklin that you see first in my line-up on the left. But death masks have also been made of the notorious, like the one of Jesse James, Old West outlaw, bank robber, and gun slinger (see second photo).
If you're anxious to learn more, a good place to start would be at Undying Faces. (Be warned, there is a photo of two men making an actual death mask from a corpse.)
You can see Beethoven's life mask here.