iMac FaceTime HD camera shows no image/black image
I have had this problem in the past. I found my answer here. http://osxdaily.com/2013/12/27/fix-there-is-no-connected-camera-error-mac/
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 &quot;No matching processes were found&quot;, this should be fine). That should do the trick.