This is a special technique to do impostors. Instead of only storing the color of the object they also store the depth and the normals. The abstract:

“We propose to render geometry using an image based representation. Geometric information is encoded by a texture with depth and rendered by rasterizing the bounding box geometry. For each resulting fragment, a shader computes the intersection of the corresponding ray with the geometry using pre-computed information to accelerate the computation. Great care is taken to be artifact free even when zoomed in or at grazing angles. We integrate our algorithm with reverse perspective projection to represent a larger class of shapes. The extra texture requirement is small and the rendering cost is output sensitive so our representation can be used to model many parts of a 3D scene. “

Link to paper and more screen shots:
http://artis.inrialpes.fr/Publications/2006/BD06/