User Zlig has set you on the right track, marcus.li!
Use all relevant suggestions from http://support.apple.com/kb/HT2090
(Apple has changed the built-in camera's name on newer Macs from "iSight" to "FaceTime" and then to "FaceTime HD." Regardless of the name of your Mac's built-in camera, the same info and troubleshooting applies.)
Be sure to test more than one camera app in more than one user account. Do NOT use the "Guest" account for this test. If you do not have more than one user account for the testing, create a new one now. (A "Standard" account is all you need for testing.)
If your problem persists with more than one Apple App in more than one user account, use Apple's final "Troubleshooting" suggestion:
"... contact Apple or an Apple-Authorized Service Provider for service."
Message was edited by: EZ Jim
Mac OSX 10.8.3