Richard Kaye has been posting some interesting photos up on Flickr using the slit-scan technique. A full description is at that link but if you think about the effect produced by moving a document over the glass of a photocopier as it’s making a copy it’s a sort so similar thing.
Here’s a few of his photos taken from this set with his explanations.
A more complex image formed using the slit camera by rewinding the film and simultaneously panning the camera. Vertical lines are formed by irregularities in the rewind. Horizontal lines are by irregularities in the panning.
Here’s the camera Richard used to produce all these:
Click on it for more details and notes, but it’s a pretty simple operation. I may well try it myself!