Google Images - Google Images is a search service owned by Google that allows users to search the World Wide Web for image content.
isk-daemon - isk-daemon is an open source database server capable of adding content-based (visual) image...
SauceNAO - SauceNAO is a reverse image search engine.
IQDB - Multi-service image search
TinEye - Reverse Image Search to help find an image's source, duplicates or altered versions.
Yandex.Images - search for images on the internet, search by image