If you created the object with bryce primitives you are out of luck, they dont export.

You can do a background pic in poser in a number of ways.

1. The infinite cove freebie at runtimedna.
   2.  Use the square primitives , rescaled, with an image map applied.

The figure will always be in front of the background.

You could do a pic of just the alter, apply it to a square and use transapency map to leave only the altar shape. Position it between the camera and figure for a depth effect.