http://vimeo.com/8778788

Here is description for this nice project:

"In this video, circle particles fill the volume of the building and once settled in place, create an image.
The trick here is to render the particle system twice. First, run the simulation and record the colour values of all the balls once they’ve settled and then to render again the second time and since the simulation is identical, the balls fall into the right place with the right colour."

If someone has tried something similar with fisica library in processing, please let me know and post links to anything you think might help me..