The campaign worked like this: canvases with the image of a bare tree were placed across 132
crosswalks in 15 Chinese cities. With green paint placed on either side, as pedestrians crossed, their shoes picked up the green, creating a trail of leaf-like footprints on the canvas. The resulting images of leafy green trees were hung as billboards in several urban locations, but what's truly incredible to think about is that DDB estimates that nearly 3,920,000
people passed through the installations while they were up. That's an enormous amount of people not only viewing the trees and their message, but contributing to their creation as well.