Legend has it that when Buddha dies his shadow was still present in his cave for hundreds of years. By shining the light onto the platform Buddha's shadow suddenly appears without an object blocking the light.
2) Platon (german)
Plato's allegory of the cave deals with the mistake to look for truth in the reality that surrounds us. To get to the truth in this scenario (P____N) one has to point the light onto it (PLATON). This symbolizes Plato's metaphor of the prisoner leaving the cave and looking into the sun to finally understand that there is more to the world than what he knows.
A shadow is always a projection of the past. In this scenario however the seed's shadow represents its future. When given enough light it will grow into a tree.
The fiducial markers are covered with 3 layers of color-filtering film to make them invisible to the human eye. Only a camera with an infrared light and infrared filter can detect the marker. This makes it possible to "glue" projections to a specific location.