Tesseract - Tesseract is an optical character recognition engine for various operating systems
TinEye - Reverse Image Search to help find an image's source, duplicates or altered versions.
GOCR - GOCR homepage. GOCR is an OCR (Optical Character Recognition) program, developed under the GNU Public License.
GImageReader - gImageReader is a simple Gtk/Qt front-end to the Tesseract OCR Engine.
TextGrabber - Office & Productivity
Yandex.Images - search for images on the internet, search by image