Where ever the person moves to corrispond to where the foot print is will make it go away, the person does not need to stamp too hard as the presence of them been in the square will after a few seconds make the foot print go, with a big green welly doing a motion simlar to a mony python scetch.

To avoid a person covering two squares at once will have to implement a command that only a square that is clear may show a foot print.

Every time a stamp/time laps, on a foot print happens it would a be a hit for the web site to show some form of a thermomiter/tree clouring as it reaches the top to grow another tree/flower/veg.

Either split the screen on the main stage to show facinating facts to the public about Carbon munitions/plants/growing veg and the planet, or have the information in a transparent form between the clouds and ground.

The person could be an animation of person throwing seeds, The animation of the plants could be a scrolling effect from right to left with it been duplicated and to run indefinatly.

Where to get the information about facts etc:

Carbon Munitions- London company called Feral International, spoke to a spokesperson from there and they are more than happy to supply facts about carbon munitions and other related topics.

Veg Facts- Contact the digit/bbc contacts to enquire about a database on veg/flowers facts that they show on there web site.