Death masks and life masks were kind of the photographs of their day. They could be used to approximate portrait paintings after a person's death, to get a more realistic depiction of the person, rather than relying on previous portraits.
They were still in use up until the 1800s before photographs began to take over. People like Napoleon Bonaparte, Thomas Jefferson, and Ludwig von Beethoven had life masks and/or death masks made of their faces in the early 1800s, shortly before photography became possible.