Oh, since you asked how it was known that the girl in the photo was 17 (with 3 children) and in your next post you quoted Carolyn Jessop, I thought you meant that Carolyn Jessop was the girl in the photo (whose name is Carolyn Young)
Oh, they must be the same person then, because the girl in that photo is Carolyn Jessop.
But she was 18 when she married.