According to Jonathan Zdziarski, an Apple iPhone hacker and programmer, your Apple iPhone handset spies on you, but it doesn’t do it on purpose as it constantly takes screenshots of the display due to design decision by Apple.

What happens is…” the iPhone takes a snapshot of your most recent action, for aesthetic reasons: after tapping the “home” button previously viewed application window undergoes a minimize effect before closing, with the snapshot being taken in order to achieve the window shrinking effect.”

Thses snapshot are constantly erased but according to Jonathan Zdziarski, forensic analysts have successfully implemented this method while investigation serious crimes such as murder, drug distribution and rape.

Source — iphoneworld