If you create a white solid in a 3D Composite, then you can project onto it using the “Stained Glass” effect located in the layer panel. Let’s say you wanted to project a photo onto the white solid. Import your photo and then create a white solid. In the photo’s “Layer” panel, you would enable the “Stained Glass” effect and also make this layer “Invisible to Camera”. Then, make sure the white solid is receiving shadows. Position the photo layer so it’s its image is now projected on the white solid. It’s invisible to the camera, but, the image is now on the white solid. From there you can experiment with a number of different effects.
Hope that helps.