I updated my MacBook Pro (15-inch, Mid 2009) to OS X 10.11 El Capitan. Then I found that the built-in iSight camera wouldn't work in any application I tried. What can I do to resolve this?
Turn off the computer. Press shift, control, option, and the power button at the same time for 15 seconds. Then turn on your computer. This resets the hardware.
Try using Disk Utility to repair disk permissions. Open Disk Utility, select your drive, select repair and then click Repair Permissions. This may fix your issue, but if not, I'd say that it's a software bug and all you can do is report the bug to Apple and hope that a fix will come soon.