Joe can you render the second (foreground) image with an "alpha channel" masking the gray area?? i'm thinking this would speed up the process.

i'm thinking you'd be able to then record an action that calls up the channel, opens the animation frame and pastes it as a new layer and does a "save as" merged and flatten (hopefully giving you the image you want)

the "alpha channel as mask" would simplify this a hecka' lot as you would not have to try and remove the gray area... i just don't know much about 3D apps.

hopefully some others will jump in on this thread and help my though process.

:)
scott