As Wikipedia says, "The Mandelbrot set is the set of complex numbers 'c' for which the sequence does not approach infinity. The set is closely related to Julia sets (which include similarly complex shapes) and is named after the mathematician Benoit Mandelbrot, who studied and popularized it. Mandelbrot set images are made by sampling complex numbers and determining for each whether the result tends towards infinity when a particular mathematical operation is iterated on it. Treating the real and imaginary parts of each number as image coordinates, pixels are colored according to how rapidly the sequence diverges, if at all.".
This is a small FLT module which can be run on most CHDK cameras to render these images, as shown below.