IrfanView - IrfanView ... one of the most popular viewers worldwide.
Greenshot - Greenshot is a free and open source screenshot tool that allows annotation and highlighting using the built-in image editor.
XnView MP - XnView is a free software that allows you to view, resize and edit your images. It supports more than 500 different formats!
Shutter - Shutter is a feature-rich screenshot program.
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
Snipping Tool - Use Snipping Tool to capture a screen shot, or snip, of any object on your screen, and then annotate, save, or share the image