New Scientist said:
ZOOM! Enhance! Manipulating blurry digital images in TV programmes like CSI often produces unfeasibly clear pictures of a suspect's face, but it turns out that it is possible to extract important forensic details from shadowy images after all.
Light shining through a window often creates what looks like shadows on the wall opposite. These patterns are in fact images of the world outside, with the window acting like a poor-quality aperture on a camera. However, the light rays are too dispersed for the image to be discernible.
Hmmm... very bad for ransom photo in the future....