Dual photography

In the category "wow, amazing science"...

Imagine a light source coming from one end and a camera picking up the image reflected by some scene. With a mathematical transformation, it is possible to reconstruct the "dual" image, i.e. the view of the scene as if the roles of the camera and the light source were reversed (note that this requires a scanning light beam, not a floodlight).

Amazingly, this allows you to see things which are not visible from the original camera viewpoint. See the video at the bottom of
this page.