In iOS 7, the wallpaper appears to be behind the icons. Can we use parallax to estimate this distance?

The Physics Behind the Magical Parallax Effect Running Your AR Apps What magic does Apple use to turn a 2-D image into something that looks like it is there in real life?

Parallax is the apparent shift of an object as your point of view changes; this is one of the advantages of two eyes — better depth perception thanks to parallax.

Parallax is the observed displacement of an object caused by the change of the observer's point of view. In astronomy, it is an irreplaceable tool for calculating distances of far away stars.