Irfanview is a free image viewer for the Windows platform with a small footprint that can display almost any still image format.
With plug-ins it can also deal with sound and video files but to my mind its real strength is it’s ability to simply and easily walk through directories of images and perform rudimentary operations against the files such as resizing and reorienting them.
It can also handily capture screen shots and crop images in a basic way.
A great value for the price (free!).