By being able to follow the viewer with the front side camera, developers can build apps that know which direction the viewer is looking at the screen. When the viewer moves, so does the perspective.

Head-Coupled Perspective on Mobile Devices. We track the head of the user with the front facing camera in order to create a glasses-free monocular 3D display. Such spatially-aware mobile display enables to improve the possibilities of interaction.
It does not use the accelerometers and relies only on the front camera.

The demo with the targets has been inspired by the work of Johnny Lee with a Wii remote.

Here’s a video via MacStories: