Next - it would be handy to detect motion in certain areas of the screen. The following example detects motion in each corner of the camera's picture - like a 2x2 grid.
Each corner plays a different sound when you wave your hand in front of it. Now - it's not the best sort of detection by any stretch of the imagination, but have a bit of a play and see what you think...
Area Detection example 1
Have fun playing many tunes...!