David Rokeby - Surveilance Art

http://www.davidrokeby.com/watch.html

quoted from website:
The video processes both present distortions of the perception of time. In one, the only things visible are things that are standing still. The effect is that of long-exposure photography, except that the image is truly live, changing subtly at every video frame. People that are moving are blurs or fogs across the image. People that are still are seen clearly.
The second process is the conceptual inverse of the first. People are only visible if they are in motion. They float as outlines of themselves in a dimensionless void, and disappear again as soon as they are still. The two images are projected with the first image beside the second, and with the second image flipped horizontally to mirror the first image.
When the images are in this state, they are mutually exclusive. A person cannot exist in both images at once. The relationship between the two images may in fact be difficult to discern.

In the 2008 version, the processes changed again. One one side, things that are moving are blurred and things that are still are in focus. On the other side, things that are still are blurred and things that are moving are in focus. The motion and stillness sides switch channels at regular intervals, causing a cross-fade in which moving things fade into the future and where fog of motion condenses into visibility.