It has happened twice recently that my iSight camera was stuck.
First, I tried to use video-chat in Skype and got nothing, just a big black square. Confirmed it with PhotoBooth; camera light turned green like it thought it was working, but did not. I confirmed that About This Mac -> More Info could still really see the hardware.
The second time, I was cold-booting (a rare event — except for the Ethernet problem that I’ll post later) and the green light came on and nothing I did would make it turn off. It was like when Peter claims that The Man is ALWAYS WATCHING (or listening through powered-off cell phones).
So I covered up the lens to keep The Man from watching me eat my cereal and debug my computer…Google found several suggestions which I tried all at once and both times, the problem was fixed:
1. First shut down, unplug, take out battery, and Wait A Little While.
2. Turn it on.
(Optional: Hold down power for a long time when it is off, it should make a curious long boot sound, but this did not seem to work either time, so it is safe to ignore. Maybe for older computers.)
3. Immediately after boot-sound, reset PRAM by holding command-option-P-R all at the same time.