+prevent the system from sleeping when a user is looking at the screen.
+
+this is accomplished using the built-in camera on my laptop screen's top bezel
+and opencv to detect a face. i'm going to use the API used by the default movie
+player in ubuntu for preventing system sleeps.
+
+OTHER IDEAS:
+1. detecting a face could simulate user activity. this would prevent sleeping
+and bring up the password prompt when the system is already asleep.
+ * how cool would that be? if the system is asleep and you sit down at it, the
+ password prompt comes up before you touch anything!
+ * or if the screen saver doesn't lock the screen, then the laptop just wakes
+ up.
+2. authenticating a user based on face recognition (as opposed to face
+detection)
+ * much more difficult to do reliably
+3. be more aggressive with turning off the screen. dim the screen as soon as
+it's not being looked at. turn it off soon thereafter.
+ * could be enough to save battery. would need to power the camera sometimes,
+ but would save on backlight. need to test.
+4. don't prevent sleep when face is detected, but user isn't actually looking at
+screen.
+ * requires pose estimation.
+ * also requires estimating the direction of the eye.