The program known as "Paint," in Windows 1.0 and Windows 6 (aka Vista).
"Photoshopping" became a household verb some time ago. But much simpler software did much simpler things on a smaller and more primitive scale. What was the very first program to offer a graphical user interface for a would be artist to create graphics? It wasn't Microsoft Paint, which has been on almost every version of Windows since the beginning. It wasn't MacPaint, which was heavily vaunted in a 1983 magazine advertisement showing how it could be used to create illustrations of sneakers. According to the information I've found, it was SuperPaint, conceived by Richard Shoup in late 1972 at the Xerox PARC, the same facility that brought us windowed operating systems, mouse driven interfaces, and other technologies we take for background today. And Superpaint, like Photoshop, could start with a digitized image (gleaned in this case from video input) and work from there.
Photon Paint (on the Amiga, 1987) and GEM Paint circa 1988 (GEM was a Mac-like operating system for IBM PCs.)
Paint programs may seem like a foregone conclusion (I programmed a simple one myself in BASIC in 1983) but some pretty impressive artwork can be created with them. The process is sometimes referred to as "pixeling". Pictured are some screen shots of various examples of the programs. A future entry will illustrate the artworks themselves.
The famous "Geisha woodcut" MacPaint drawing, and the Overlord* himself in 1984 with MacPaint front and center (according to folklore, he isn't wearing any pants!)
*That's Steve Jobs, to you non-Mac owners.