CamFind - CamFind is the very first mobile application that can photograph, identify, and provide information...
TinEye - Reverse Image Search to help find an image's source, duplicates or altered versions.
IQDB - Multi-service image search
GImageReader - gImageReader is a simple Gtk/Qt front-end to the Tesseract OCR Engine.
Yandex.Images - search for images on the internet, search by image
NISE - The NISE Image Search Engine is a reverse image search engine (like tineye.