"AlWAYS" use a Totally Black (0,0,0) Background for use with Masks(In your Sky Library there is a totally black background),That way there will be no fuzziness...Use the Mask option in Bryce to render your Trees... Why not do it the other way around?I do it all of the time,Bring your Mojoworld image as a background applied to a 2d square/Plane and then build your scene around your image?I understand that you really want to do it the other way around and all but you wont be able to get the realistic Shadows doing it your way unless you want to spend hours doing it in Photoshop? BTW..I am in the process of Modeling Trees for Mojoworld and as soon as I get enough time I will finish the Models(Tooooo many projects going at once...Dought!)I have been told about the Poly count used in Mojoworld and I am trying a work around and I am almost positive it will work..We will see...I hope you find your answer....