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Silke sent in the "Aura Cabinet" which utilizes an Arduino to project images onto fog, creating an aura-type image. It look really interesting, and there is a video available here, but be warned, the video has a horrible high-pitched tone throughout.

By means of Processing the visitor is tracked by camera. His picture is compared with an reference picture of the background. The colour differences will be reported in a kind of silhouette. Depending on how near the visitor steps to the glass cabinet, within a certain tact recurrently new pictures are generated and illustrated. These new pictures are assimilated to a small collection of pictures while older pictures are replaced by them.

More about the Aura Cabinet [Translated Version]