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Proceeding from Cohen's initial question "What are the minimum conditions under which a set of marks functions as an image?", AARON has been in continual development since 1973. The name "AARON" does not seem to be an acronym, rather it was a name chosen to start with the letter "A" so that the names of successive programs could follow it alphabetically.
Initial versions of AARON created abstract drawings that grew more complex through the 1970s. More representational imagery was added in the 1980s; first rocks, then plants, then people. In the 1990s more representational figures set in interior scenes were added, along with colour. AARON returned to more abstract imagery, this time in colour, in the early 2000s.
AARON initially drew in black and white using a succession of custom-built "turtle" and flatbed plotter devices. Cohen would sometimes colour these images by hand in fabric dye (Procion), or scale them up to make larger paintings and murals. In the 1990s Cohen built a series of painting machines to output AARON's images in ink and fabric dye. He now uses a large-scale inkjet printer.
Development of AARON began in the C programming language then switched to Lisp in the early 1990s. Cohen credits Lisp with helping him solve the challenges he faced in adding colour capabilities to AARON.
An article about Mr. Harold Cohen appeared in Computer Answers, describing AARON and showing two line drawings, some of his work has appeared in the Tate gallery that summer. The article goes on to describe the workings of AARON, then running on a DEC VAX 750 minicomputer. 
Raymond Kurzweil's company has produced a downloadable screensaver of AARON for Microsoft Windows PCs. This version of AARON can also produce printable images. AARON's source code is not publicly available, but Cohen has described AARON's operations in various essays and it is discussed in abstract in Pamela McCorduck's book.
AARON cannot learn new styles or imagery on its own, each new capability must be hand-coded by Harold Cohen, but it is capable of producing a practically infinite supply of distinct images in its own style. Examples of these images have been exhibited in galleries worldwide, the exhibitions serving as an artistic equivalent of the Turing test. It does seem however that AARON's output follows a noticeable formula (figures standing next to a potted plant, framed within a coloured square is a common theme).
Cohen is very careful not to claim that AARON is creative. But he does ask "If what AARON is making is not art, what is it exactly, and in what ways, other than its origin, does it differ from the 'real thing?' If it is not thinking, what exactly is it doing?" — The further exploits of AARON, Painter. However, it could be argued that AARON is simply following procedural instructions and that the real artist behind each piece is AARON's creator, Cohen. Adding further weight to this argument is AARON's seemingly narrow 'library' of human form variations, poses and scene compositions and the requirement of hard coding to add new 'styles'.