Just got my answer from metacreations, and it doesn't look good for my plight. Oh, well. Here's the text from their answer to my case: "There is no real way to place an image as a background in Bryce. You can try placing the image on a 2D plane that fills your background or try mapping it on other types of objects for a similar effect. However, you will not get the sun or moon to show infront of this object and this limits its usefulness. It is also possible to get odd shines or reflections off the plane based on the lighting situation in your scene and due to there actually being an object there to hold the background scene."