Just about every Mac comes with a camera today. It works like a charm but a frustrating error can appear from time to time. I had this annoying experience after several sleep modes with a sympatic black screen saying “There is no connected camera”.
Obviously nobody disconnected your camera and here is a good news. You don’t need to reboot your mac anymore!
Just open a terminal, enter the following commands and press enter.
sudo killall VDCAssistant
sudo killall AppleCameraAssistant
The first command can be enough. Actually I always use that one only.