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Full user review
"Best free image viewer available."
Free. Small file, loads fast, no bloatware. Displays images fast using nearly any extant format. Offers easy resizing for e-mail and web use. Can do some photo editing, but this isn't really what you use the program for. Many other features.
What cons? See above.
I wouldn't be without IrfanView. Small enough to work on nearly any PC and with older operating systems. Have used it for years and it keeps getting better. If you really like this program, send Irfan a donation to keep it going.