I would like to project some text into a real scene and have a rock solid tracking, a shadow caster object and my lights set up.
Now i seem to overlook the setting to turn a second object invisible to it only receives the shadow casted by the text.
Do you want the casting object to be invisible so that you only see a shadow being cast on a surface?
Or do you want the receiving surface to be transparent except for the shadow area?
If it is the first option, you should be able to turn off the visibility of the object in the geom menus.
If you want to hide the shadow receiver surface, you can simply turn it off. What you will need to do is output a separate shadow pass and recomposite the 3D shadow on top of the background with the object.