extropia.com
Adobe Photoshop is hands down, the most popular program for creating and modifying images for the web.
This is true not only because Photoshop is available on a wide array of platforms ranging from Mac to Windows to UNIX, but because after four generations of development, Adobe Photoshop has the most intuitive user interface, the most complete set of tools, and the largest number of reference books around.
In fact, as Deke McClelland says in Photoshop 3 Bible, "Some estimates say that Photoshop sales exceed those of all of its competitors combined."
Photoshop is only one tool in a good designer's arsenal. Other popular tools include Paint Shop Pro, DeBabelizer, or LView Pro for Windows and GIF Converter or Graphics Converter for Macintosh. Fractal Design, Aldus and HSC also put out some excellent programs
Kenji Tachibana (a gifted freelance graphics artist) and I decided to focus on Photoshop primarily because Photoshop is the program that most web designers use.
However, since most programs these days use similar concepts, many of the things we talk about here will be directly relevant to any other graphics program on the market.