The inbuilt iSight video camera wasn't working in Skype or PhotoBooth. In both cases it was giving an "
No video camera detected" error message.Rummaging around turned up this note that confirms the console view that there's a missing QuickTime file. This is how to fix it:Close the relevant apps, then running the following (from a Terminal window) entering your account password if required:
cd /System/Library/QuickTime/QuickTimeUSBVDCDigitizer.component/Contents/MacOSsudo chmod 755 QuickTimeUSBVDCDigitizer
And relaunch the programs using the camera.