This extension let you search for image variations using the reverse image search engines of your choice. You can search them individually or several at once, according to your preferences in the options window.
TinEye.com is the first, most extensive engine (with a database nearing two billion images), and give the most straight-forward accurate results. It is developed by Idée, a Canadian company based in Toronto, and it's official extension is TinEye Reverse Image Search.
Google Search by Image was launched in June 2011 and replaced the defunct GazoPa in this extension.
GazoPa.com implements a more loose similarity search, that sometimes produce very intriguing results from it's database of hundred million images. It is developed by Hitachi America in Santa Clara, California, part of the Japanese mammoth corporation. It's flag extension is GazoPa Similar Image Search.
Cydral.com, located in Guyancourt, Île-de-France, dream of the big league while offering filters for adult material and other content types. It's home add-on is Cydral Image Search Engine.
Yandex.ru, the leading web portal in Russia, offering variety of web services from it's offices in the Leo Tolstoy St., Moscow, sometime succeed where other fail, producing images from multitude of Russian private forums dedicated to visual culture. It's unofficial reverse image search extension is Who Stole my Pictures?, a private venture that extended to support most other engines.
Baidu.com, whose literal meaning is "hundreds of times", took it's name from a 13th century poem about the search of beauty. Located in Beijing, it focus it's text and multimedia searches on the Chinese speaking web. It's unofficial add-on is Reverse Image Search.
IQDB.org, SauceNAO.com and Ascii2D.net are three minor Japanese engines that specialize in Manga images. They might be added to this add-on in the future and are currently supported semi-officially by Image Search Options.