TinEye - Reverse Image Search to help find an image's source, duplicates or altered versions.
Capture2text - Capture2Text enables users to quickly OCR a portion of the screen using a keyboard shortcut.
GImageReader - gImageReader is a simple Gtk/Qt front-end to the Tesseract OCR Engine.
TextSniper - Instantly extract any text from your Mac's screen
Yandex.Images - search for images on the internet, search by image
dpScreenOCR - Program to recognize text on screen