A picture that can change its shadow
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.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.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.
Photos with shifting shadows come to life [New Scientist via Gizmodo]

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Isn't this just a transmissive form of a lenticular? And wouldn't it cost the same, if not more? Why haven't billboard manufacturers used lenticulars already? Because they're not cost-effective?
Glad to hear New Scientist realizes the importance of this...to the advertising industry. >:^o
Billboards (or at least the Clearchannel/highway specials) I worked with were printed at usually less than 100 dpi.
I'll bet that it's cheaper (because they do it in bulk) to just put up those gigantic LED billboards that are cropping up more and more, and just wire in some photo sensors that will detect the position and intensity of the light and display the appropriate picture.
i'm still waiting for bob shaw's slow glass ("light of other days", 1966)
I'm a Londoner, but I still find the kind of accent that the presenter woman had quite hard to follow.
What kind of an accent is it? Does anyone know?