Adobe Photoshop is the market leader in photo editing software. Originally designed by John and Thomas Knoll in 1987 for the Macintosh, the program has grown into the industry standard for computer graphics today. Many of the most well-known features of graphics programs in use today were originally pioneered by the Photoshop system.
The first full release of Photoshop was under the Knoll Software name, before they completed their partnership with Adobe. The first edition of Photoshop, including the manual, fit on an 800k floppy disk with room left over. The Macintosh computer was the only place you could run Photoshop, from the first release in 1990 until version 2.5 was finally released for the PC world in 1992.
One of the real power features of Photoshop has been modular design. The programmers wanted to be able to make changes without altering the core engine, and along the way, they opened the ability to create filters and add-on modu0les that greatly expanded the power of the program.
Photoshop continued to add new features and power over the years. Layers were added to the program in 1994. Macros and adjustment layers arrived in 1996. 1998 saw the invention of the Magnetic Lasso and the addition of the History palette, which allowed for undoing several actions, not just one. The Healing Brush, a powerful cloning tool, was added to the lineup in 2002, as well as the first support for the RAW format.
Version CS2, released in 2005, has a variety of new feature, including red-eye correction, lens correction, HDR support, and the latest revision of support for the RAW format.
Photoshop is so well known that it's name became a verb, much like Google has done. However, since Adobe would like to protect the copyright on Photoshop, many websites have slightly changed the phrase to "photochop" instead.