Pics go on 2d planes, not sure what you mean by putting something across it. Lots of people render trees then put them back into a bryce scene as background trees on a 2d plane. This reduces the poly counts and time consuming rendering of stuff which is further back from the camera. But it can also work up close too. There's several people here who have done this very well. And its not just good for trees. Only thing is the plane needs to be at a 90 degree angle with the camera (I think) so if you put one in then change the view it could mess up the scene. HTH