OS X Yosemite: Use the built-in camera

If your Mac or display has a built-in iSight, FaceTime, or FaceTime HD camera, you can use it to take pictures or videos using Photo Booth, make video calls using FaceTime, or video chat with your friends and family using Messages.

• Turn the camera on:
  A green indicator light beside the camera glows when an app that uses the camera is open.

• Turn the camera off:
  Close the active app window. The green indicator light turns off, showing that the camera is off and video has stopped.