CSS Zen Garden listed this effect under 'Clever Designs'.
CSSPlay.com has dedicated several pages 'Fun with Background images' evolving my original idea.
Below written by Stu Nicholls - CSSPLAY
Recently I was prompted to take a look at a couple of Zen Garden entries by Tony Forsey.
Now I hadn't seen this effect on web pages before and had a quick burst of ideas as to how this could be put to further effect.
The above examples are the outcome of my imagination, but they are all as a result of the original idea by Tony who was first to discover the possibilities.
Stu Nicholls - CSSPLAY