PhotoSearch - Search Photos for hashtags and users. Browse and explore public Images.
PicsLikeThat - This is a visual and semantic image search system finding images on Fotolia.
lingvist.info - News & Books
IQDB - Multi-service image search
Yandex.Images - search for images on the internet, search by image
isk-daemon - isk-daemon is an open source database server capable of adding content-based (visual) image...