isk-daemon - isk-daemon is an open source database server capable of adding content-based (visual) image...
Yandex.Images - search for images on the internet, search by image
IQDB - Multi-service image search
TinEye - Reverse Image Search to help find an image's source, duplicates or altered versions.
SauceNAO - SauceNAO is a reverse image search engine.
PicsLikeThat - This is a visual and semantic image search system finding images on Fotolia.