The recognition engine automatically pinpointed unique landmarks by sifting through 42 million images from photo-sharing websites Picasa and Panoramio, as well as online travel guides. Visual algorithms compared and filtered landmark images taken from different angles and under many lighting conditions.

GPS tags in many of the images also allowed the engine to identify landmarks through geographical clusters of photos. For instance, a bunch of uploaded images from many different sources regarding a certain iron tower in Paris, France would become flagged as a prime landmark candidate.

Google's team continues to try and improve on the engine's 80-percent accuracy. Visual images which pose no problem for humans can still easily baffle computers -- in one case, the engine has been known to accidentally identify an image of the American flag as the New York Stock Exchange and its flag-draped walls.

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