If that is the case, The question is how can I Turn on a MacBook Camera?
Well, no need to panic or worry.. the build in camera it is activated by software requesting camera input. If a piece of software is not up to date, the application may not be able to turn on the built-in webcam.
Your webcam turns on and off properly by using the Photo Booth application.
The here is a step by step on How to Turn On Camera on MacBook Pro
Click the “Finder” button in your MacBook’s desktop application bar.
Click the “Applications” folder on the left side of the dialog.
Scroll down to the “Photo Booth” icon, then double-click the icon to launch the program.
Wait until the green LED lights up next to the camera. Your built-in iSight camera is now on.
If your MacBook’s built-in iSight camera does not turn on automatically when entering Photo Booth, then you may be experiencing a hardware issue and should take your MacBook to a certified technician or Apple store for check up.