Apple - iMac FaceTime HD camera shows no image/black image

I have had this problem in the past. I found my answer here.

Open terminal from the utilities folder in the applications folder. Type sudo killall VDCAssistant into terminal and click enter. Then, enter sudo killall AppleCameraAssistant (may say "No matching processes were found", this should be fine). That should do the trick.

Resetting the SMC solved the camera issue. It's now working as per normal.

All that involves is shutting down the machine, removing all power from the computer for 15 seconds, and restoring power.