Unusual effects can be obtained using random numbers or random transformations to produce either unusual graphical pictures or computer animation if a sequence of such pictures change over time. Early on, there were examples of such animations using analogue computers (John Witney: Permutations, 1966) and from Computer Image.
A good introduction to the use of randomness can be found in Les Mezei's paper Randomness in Computer Graphics.
Early attempts using a microfilm recorder were described by Michael Noll in a paper Computers and the Visual Arts in 1967. He makes the point Art has always depended upon science and technology to supply both the medium in which the work is done and the tools for doing it. He gave as an example a line drawing called Gaussian Quadratic:
In another paper Human or Machine he challenged a 100 students to recognise a Mondrian from a computer-made random artwork.
In 1970, Ken Knowlton defined a new computer animation language called EXPLOR (EXplicitly defined Patterns. Local Operations and Randomness) which could produce computer animations on a 340 × 240 grid. The user was able to define patterns and provide transformations over time that could include randomness. The language did not require the user to be proficient in the usual computer languages like FORTRAN so artists could explore with EXPLOR. The paper EXPLOR - A Generator of Images from Explicit Patterns, Local Operations and Randomness describes the language and gives examples.
Ken worked with the artist Lillian Schwartz on a number of projects and Lilian's paper The Artist and Computer Animation gives her views on using Ken's system.