Greenshot - Greenshot is a free and open source screenshot tool that allows annotation and highlighting using the built-in image editor.
ACDSee - ACDSee is an image viewer that uses very little system resources, and it has a small, sleek size that won't take up much space on your system.
ShareX - ShareX is a free and open source program that lets you capture or record any area of your screen...
digiKam - Professional Photo Management with the Power of Open Source
LightShot - The fastest way to take a customizable screenshot.
Flickr - image and video hosting website