OS X Mountain Lion: Use your Mac’s built-in camera
If your Mac computer or display has a built-in iSight, FaceTime, or FaceTime HD camera, you can use it to take pictures or videos with Photo Booth, create movies with iMovie, or video chat with your friends and family over the Internet using Messages.
A green indicator light beside the camera glows when the camera is on.
To turn off the camera, close the active app window. The green indicator light turns off, showing that the camera is off and video has stopped.