In Second Life we tend to use open source products. But, some people use the professional products from Adobe, Photoshop being the best known. I think it has no equal. There are other image editors. But, Photoshop (PS) is the industry standard. If you plan to work for a gaming or other company that works with images, you have to know PS. But, Adobe is making big changes that will radically affect casual users.
Adobe is changing how they deliver their software. Until now they have sold their software in a package with a perpetual license. I can still use an old copy of CS3, CS4, CS5.5, and CS6. (CS = Creative Suite) It isn’t cheap. A new version of PS costs US$800. Updates can be $300 to $400 per version come every 12 to 24 months. People can find PS on Amazon and in stores for $650. But, quite often that is the ‘basic’ version not the ‘Extended’ version.