I just had to post a short exchange from a Sherlock Holmes story I was reading a little while ago. The story is "A Scandal in Bohemia," where the King of Bohemia, or Crown Prince at the time of hisindiscretion, is relating to Sherlock Holmes how he might be blackmailed by a lady he had contact with previous. At first, Sherlock Holmes is doubtful that the King need worry:
Sherlock Holmes: "I fail to follow your Majesty. If this young person should produce her letters for blackmailing or other purposes, how is she to prove their authenticity?"
King of Bohemia: "There is the writing."
SH: "Pooh, pooh! Forgery."
KB: "My private note-paper."
KB: "My own seal."
KB: "My photograph."
KB: "We were both in the photograph."
SH: "Oh, dear!"
Ha ha! Just a classic exchange.