One of the most popular subfora on reddit is /r/IAmA. Celebrities create threads that begin with "I am X, ask me anything" and invite people to ask them any question. This type of thread is colloquially called an AMA.
Bill Gates recently gave an AMA. As is standard procedure at reddit, he provided a photo to prove that the username was, in fact, him. Gates chose a novel way to prove his identity: he recreated a 46-year old photo of himself in nearly perfect detail.
Unrelated question: how many of you would show up to an AMA by the internet-famous Miss Cellania?