Under Scan is a "large scale video art installation featuring more than 1000 interactive portraits of people from London and the East Midlands." The work was created by Montreal-based Mexican artist Rafael Lozano-Hemmer.
It transformed public space of Trafalgar sq "into a new site of exchange". On entering the flood lit area in front of the National Gallery, people are detected by special tracking system. Moving across the square they encounter interactive video portraits cast within their shadows. "The piece is intended as a public takeover of a city by its inhabitants and links surveillance technology with strategies of self-representation."
I unexpectedly walked in "Under Scan" in Trafalgar sq few days ago (on till 23 November). It was great fun and kind of surreal.