Google is asking surfers with time on their hands to help it categorise and label the images indexed by its search engine, building a database of knowledge about the contents of the images.
The company launched an online game on Friday, Google Image Labeler, which it describes as "a fun way to help us organise all the images on the web". In the game, two randomly selected players are each shown the same image, plucked at random from Google's search index, and given 90 seconds to suggest as many keywords or phrases as they can to describe it. They score points if any of their descriptions match.
Google's image search engine currently returns results based on captions and other text adjacent to images on web pages, without reference to the content of the images themselves. The game will allow it to improve the performance of the search engine by returning results based on the players' descriptions of the images.
Google's game, based in part on technology developed at Carnegie Mellon University, is not even the first to use volunteer labour to categorise images: the ESP Game developed by Luis von Ahn and other researchers at Carnegie Mellon first put players to work tagging its image database in October 2003.