When a camera is pointed at a TV that is being feed a picture from the camera itself it starts a feedback loop. Usually the loop either gets very dark from not enough light or it gets very bright from too much light. Sometimes the balance is just right and it starts doing crazy patterns that include fractals.
live video feedback.wmv (200 mb)
This is a simple video of a camera being pointed at a computer monitor.
You can add mirrors, another camera, or other equipment
(color corrector, video mixer) to help with the effect.
strech2minlogo.mxf (750 mb)
This is video feedback not using a camera but FFrend a VJ clip making
program.
This was not done with a camera but entirely with a free program called FFrend (http://ffrend.sourceforge.net). The brightness can be controled better and other video fx can be added. FFrend will let you automate the parameters as well, giving you even more control.