Faststone (For Windows only)
A fast, stable, user-friendly image browser, converter and basic editor. Includes image viewing, management, comparison, red-eye removal, emailing, resizing, cropping and colour adjustments. Gives access to EXIF information. Supports all major graphic formats (BMP, JPEG, JPEG 2000, animated GIF, PNG, PCX, TIFF, WMF, ICO and TGA) and popular digital camera RAW formats (CRW, CR2, NEF, PEF, RAF, MRW, ORF, SRF and DNG).
I use this as an image browser and can highly recommend it. I do not use it for conversion of files, or any image editing, so cannot comment on those features. However, compared with ACDsee, the commercial image-browsing program (an old version of which I have) this works just as well, and is superior in some respects.
There are many other image viewers available, both paid-for and freeware. Wikipedia publishes a useful table giving basic comparisons between them all.
Irfanview (For Windows only)
This is another excellent image viewer/browser which I can recommend. This multimedia and graphics viewer can handle any type of file you throw at it: from GIFs to Real Audio to MP3 to Adobe Photoshop files, as well as a lot of obscure formats too.
I have used this program but, to be honest, I find it has too many features that I don’t need … and am never likely to. As a result, I have long ago uninstalled it. I much prefer Faststone which does everything I want, and more simply. It’s horses for courses.
Visipics (For Windows, Linux)
One of the problems with digital photography is that it’s so quick and easy, you end up huge number of images. Then you edit them, tweak them, re-size, save and re-save … and before you know it, your hard disk is bursting at the seams.
It’s a safe bet that quite a few of the images you have on your disk are duplicates. Visipics is quick and easy-to-use program that finds all your duplicates and allows you to delete them.
For more photographic freeware see here