. PNG format doesn't need any exceptional software for opening?
Never been a problem for me. It's THE most common lossless compression imaging format on the Internet.
EDIT: Just too clarify some of my comments I'm suggesting using .PNG specifically when posting a photo to a site such as Facebook due to the additional, and sometimes
dramatic, compression such sites often employ. I mention FB in particular because it's compression algorithm can be particularly harsh. What I'm definitely not suggesting is that .PNG should be used in place of .JPG across the board. Not all JPG's are created equal and a really good .JPG can be a wonderful thing, relatively speaking.
That being said, there will always be a certain juggling act between file QUALITY and file SIZE (in megabytes) you'll have to consider when posting/hosting images online. Using the .PNG file format is one to way to help offset brutal compression, but if your .JPG's are looking terrible, as a general rule, then you may want to look into how those JPG's are being created to begin with.
