XnView is a free image browser, viewer and converter with a lot of features. It can read more than 400 file formats for both images and video, used across different platforms like Windows, Linux and Mac. It can be used to view, organize, convert graphics and photos files or to create slide show, contact sheet, HTML pages, etc.
Besides popular formats like JPEG, TIFF, GIF, BMP, AVI, MPEG, and Quicktime it can also read older formats such as targa (TGA) and supports 44 languages. XnView can handle other tasks such as scanning (built-in TWAIN support). The developers thoughtfully included handy screen capture and slide show features. Metadata embedded in images (such as EXIF) is shown.
You can also view a histogram of the image. I like the customization of menus and extensibility of the software through plug-ins. It can perform operations like auto crop and resize, auto contrast, auto brightness, and add a 3D border and also can handle batch operations very quickly.