Ok, you'll prolly think I am nuts

This has bothered me for many moons.

You are watching a movie, and in the movie, there is a picture of one of the characters in their youth. Now, sometimes, this is a picture of some random guy. Other times, however, it is obviously a picture of the actor him/herself (from days of yore). Even more confusing, is that sometimes, the picture is obviously the actor, with ANOTHER one of the actors from the film.

How the hell do they do this? I presume that it would be pretty easy to do with one actor, since you could just pick some picture from their past. But two actors? What are the odds that not only did these two actors chill in their youth, but that pictures were taken?

Now, I can think of a few ways to handle this situation. You could Photoshop two different pictures together, to create a faked picture of the actors together… You could get some damn fine lookalikes to pose…

Anyone know how they do it for sure? Anyone care?