Greenshot - Greenshot is a free and open source screenshot tool that allows annotation and highlighting using the built-in image editor.
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.
ksnip - Ksnip is a Qt based cross-platform screenshot tool that provides many annotation features for your screenshots. - DamirPorobic/ksnip
Yandex.Images - search for images on the internet, search by image