My Macbook’s iSight camera randomly stopped working today, having worked fine ever since i’ve had it. I originally found the problem with photo booth, and went searching for a resolution. After reading numerous posts about potential fixes, I found out that you should try the following (in order of severity);

1) Double check that it isn’t limited to Photo Booth (try iChat, and check if you can take a new user picture from the Accounts preferences)

2) Make sure it isn’t limited to just your user, which would suggest a problem with your user settings. Login as someone else (create a test account if there’s only one account), and try the same applications.

3) Close and re-start the problem application.

4) Reboot your Mac.

5) Force shut down your Mac (hold shutdown key for 10 seconds)

I tried all of the following, and my iSight camera still wasn’t working. So the last resort, is to reset the SMC (Systems Management Controller) of your Mac, for which there’s a detailed guide in the apple knowledgebase:

http://support.apple.com/kb/HT1411?viewlocale=en_US

Full official apple article on troubleshooting your iSight camera is here:

http://support.apple.com/kb/HT2090?viewlocale=en_US