Windows does a reasonable job of previewing images these days, and you've probably several other image viewers that you can use, if necessary, so installing yet another isn't likely to be high on your list of priorities. And yet, it could be a very good idea. Here's why.
IrfanView isn't just one of those identikit image viewers that handles only the most common file formats, for instance. Along with the usual JPG, PNG, BMP and GIF comes support for viewing no less than 12 digital camera RAW formats, various game formats (WAD, WAL, VTF), fax files (DCX, G3, SFF) and more. The program can view icons directly (ICO), extract them from executables (EXE, DLL), even play some video and audio files.
IrfanView is able to save files in 21 formats, too. A powerful Batch Conversion dialog makes it easy to convert an entire folder structure of images from one format to another.
If you're more interested in working on individual images then you'll appreciate the paint tools, which help you annotate an image by adding text captions, drawing basic shapes, changing colours, and more. There's a reasonable selection of image manipulation tools (flip, rotate, resize, sharpen, colour corrections), and a basic set of special effects (emboss, oil painting, sepia and so on) can be enhanced by downloading additional plugins.
And the more you explore IrfanView, the more smart features you uncover. Like its slideshow feature, that can save a sequence of your favourite images to an EXE or SCR file. The batch scanning option for processing multiple images in a row. The support for editing multi-page TIFFs, or creating multi-page PDF files. And the way you can extend the program even further, by installing free plug-ins from the IrfanView site.
What's new in 4.54 (see release notes for more)?
New effect in Image->Effects menu: Insert Speech Bubbles Examples/Screenshot: speech_bubbles.jpg
New effect in Image menu: Add Shadow, Shape, Rounded corners, Snowflake etc.
New effect in Image menu: Add Hexagon (or tiles), Star, Spikes, Heart etc.
Show mouse zoom magnifier: CTRL+SHIFT + Mouse-move in the image (mouse wheel zooms within magnifier area, click inside closes it)
New border effect in "Add Frame" dialog: Broken Edge
New effect added: Radial Brighten (Effects browser dialog)
New option in Capture dialog: Draw red circle around cursor
New option in Advanced batch dialog: Set maximal dimensions for resize
Profiles option added to Contact Sheet dialog
Option to read 1 BPP images in RAW dialog
Command line: /filepattern can be combined with /slideshow
TIF/PCX/PSD loading bugs fixed (thanks to Apriorit)
Some PlugIns are changed/updated, please install the newest versions
The editing features will never compete with Photoshop, but an excellent image viewer and powerful extras mean IrfanView is still worth a serious look