By combining several hundred photographs and then printing the composite lighting differences into a grid of transparent hexagons, a group of researchers led by the Max Planck Institute's Martin Fuchs have developed these pictures that change as light moves through them during the day.
From New Scientist:
The researcher's prototype device, which can be attached to a window, comprises three layers: a lens array at the rear focuses light onto a transparency film on which a photograph is printed; the light passes through and is projected onto a "diffuser" in front, where the image is revealed.
When the Sun rises in the east, the projected image shows objects casting a long shadow to the west. As the Sun climbs towards midday, the shadow shrinks, before extending to the east in the evening.
Provided the ink or dye does not fade over time, these would work indefinitely. It's easy to think these could be the next gimmick for advertising and (as prices fall) portraiture.