Copyscape

Copyscape is an online plagiarism detection service that checks whether similar text content appears elsewhere on the web. It was launched in 2004 by Indigo Stream Technologies, Ltd.
Copyscape is used by content owners to detect cases of "content theft", in which content is copied without permission from one site to another. It is also used by content publishers to detect cases of content fraud, in which old content is repackaged and sold as new original content.
History.
Copyscape was launched in 2004 by Indigo Stream Technologies, Ltd., co-founded in 2003 by Gideon Greenspan. According to an interview with Greenspan, the company originally developed an alerting service called Google Alert, out of which the Copyscape service grew as an expansion.
Functionality.
Given the URL or text of the original content, Copyscape returns a list of web pages that contain similar text to all or parts of this content. It also shows the matching text highlighted on the found web page. Copyscape banners can be placed on a web page to warn potential plagiarists not to steal content. Copysentry monitors the web and sends notifications by email when new copies are found, and Copyscape Premium verifies the originality of content purchased by online content publishers.
Copyscape uses the Google Web API to power its searches. Copyscape uses a set of algorithms to identify copied content that has been modified from its original form.
Reported use in plagiarism cases.
Copyscape's use has been reported in cases involving online plagiarism: