Amazon's Mechanical Turk

The Amazon Mechanical Turk (MTurk) is one of the suite of Amazon Web Services, a crowdsourcing marketplace that enables computer programs to co-ordinate the use of human intelligence to perform tasks which computers are unable to do.

Requesters, the human beings that write these programs, are able to pose tasks known as HITs (Human Intelligence Tasks), such as choosing the best among several photographs of a storefront, writing product descriptions, or identifying performers on music CDs.

Workers (called Providers in Mechanical Turk's Terms of Service) can then browse among existing tasks and complete them for a monetary payment set by the Requester. To place HITs, the requesting programs use an open Application Programming Interface, or the somewhat limited Mturk Requester site.

Requesters can ask that Workers fulfill Qualifications before engaging a task, and they can set up a test in order to verify the Qualification. They can also accept or reject the result sent by the Worker, which reflects on the Worker's reputation. Currently, a Requester has to have a U.S. address, but Workers can be anywhere in the world.

Payments for completing tasks can be redeemed on Amazon.com via gift certificate or be later transferred to a Worker's U.S. bank account. Requesters, which are typically corporations, pay 10 percent of the price of successfully competed HITs (or more for extremely cheap HITs) to Amazon.

Source: http://en.wikipedia.org/wiki/Amazon_Mechanical_Turk