IrfanView (which takes its name from its creator, Irfan Skiljan) is the wise old app of image viewers. In its 13-year lifespan it’s remained one of the most useful things you can put on your PC. It’s an excellent image viewer, but it’s capable of much more than that.
You can browse through your images quickly, or watch them as a slideshow. IrfanView also includes a feature-packed photo editor, a batch file converter, and a scanner interface. If that's not enough, it's also expandable via plugins.
IrfanView is easy to master thanks to its slightly old-fashioned but nonetheless practical interface. There are copious keyboard shortcuts to speed up everyday organization and editing tasks, and the directory view makes it straightforward to drill down through folders to find the images you want.
IrfanView's 64-bit version is guaranteed to work faster and be more compatible with image files larger than 25MB.
Irfanview is exceptionally tiny in terms of the system resources it uses, and that means it’s blazingly fast. That’s important in these days of mega megapixels, which have pushed image file sizes up dramatically.
Irfanview is also very sociable. It plays nicely with pretty much any kind of image file you can imagine - not just photo ones but icons, PostScript, PSD, GIF and more, as well as music and video files. That makes it an excellent anything-viewer.
The other thing that Irfanview excels at is conversion. It has a batch processing utility for fast renaming and conversion of multiple files, and can convert from and to most image file formats with complete control over the conversion settings. Add in skinnable toolbars and support for plugins and you’ve got the Swiss Army Knife of images. It’s brilliant.