[vtkusers] image as background of render window

[John Hunter]

I have a VTKRenderWindow / VTKRenderWindowInteractor and would like to
make an image the background of this window, rather than having a
solid colored background.  I would add 3D actors to the renderer, and
these would move in 3space with the mouse interaction commands, but
the background image would remain static.

Is this possible?  

Thanks!
John Hunter

VTK4.4