Q: iSight Issues

About a month ago I had a very long Skype video chat with a friend. I thought nothing of it until today, when I tried to open Photobooth and I was greeted with a black screen. I remembered that I experienced similar trouble months ago, when trying to use Photobooth. I tried using FaceTime only to be replicated as an empty black square.

What could possibly be wrong with both Photobooth and FaceTime (but not Skype) to cause this problem.

I'm using a 2012 MacBook Pro, in case that helps.