How did Peter recognize Elijah and Moses?

> Matthew 17:3 Just then there appeared before them Moses and Elijah, > talking with Jesus. > > 4 Peter said to Jesus, “Lord, it is good for us to be here. If you > wish, I will put up three shelters—one for you, one for Moses and one > for Elijah.” I am wondering how Peter recognized that the men were Elijah and Moses? Photographs and portraits didn't exist back in those days. If they did, Peter being a fisherman wouldn't have been to school to see them. And I doubt Moses and Elijah began their conversation by saying - "Hello Jesus, I am Elijah and this is my buddy Moses." So how would Peter know it was Elijah standing there?