Where do they get the pictures of characters in movies?

I bet it wasn’t that hard to get pictures of a young Gloria Swanson for Sunset Boulevard.
I believe that in the final episode of Quantum Leap we see a picture of a young Dean Stockwell, which wouldn’t be hard to find either.

Heck, I know of a fairly low-budget Canadian movie that somehow managed to afford to license scenes from a previous film. Suck (2009) is a rock-and-roll vampire comedy, with a vampire hunter played by Malcolm McDowell. A flashback, featuring footage of a young McDowell in O Lucky Man! (1973), reveals why he has a personal vendetta against vampires.

Oh, I loved ‘O Lucky Man’ when I was, um, how old was I? I can’t remember. Anyway, now apparently I have to seek out and see ‘Suck.’ This is embarrassing.

Oh, well. ‘The Limey’ was fabulous, and, God help me, in whatever era it was, I liked ‘Poor Cow.’ I think maybe in the 60’s we admired whatever was unlike what we had previously seen. Besides, Donovan.

If magic doesn’t work right and looks very fake, sure. Or at least sometimes these pictures are clearly faked, badly. I supposed the faked good ones wouldn’t be noticeable.