ASCII is an encoding system used to convert numerical values into Roman alphabet characters and other symbols. An encoding system is necessary because computers store data in number and not letter form. ASCII is the standard system used in most personal computers today.Asciitable.com: ASCII Table

Because the earliest computers did not have the ability to render images as they do today, ASCII characters were initially used as a way to produce images on computers. ASCII art can either be still images or moving pictures.Roysac.com: The three ASCII Art Styles of the Underground Art Scene ASCII art uses ASCII characters to give a stippling effect to show areas of light and shadow. The technique is similar to the Pointillism painting style of Georges Seurat where several little dots comprise an entire image.Web Museum: Georges Seurat