Yup, I would use the edited photo as a backdrop and a guide. The photo would be the constant as would be the Bryce camera's (Director's or Camera's View) position (because it would be locked onto the photo, directly facing it) (The Bryce document size would also be the same size/aspect ratio of the photo).

The variables would be;
The Camera/View FOV.
The attributes of the cube (size and poistion in 3d space)

ALL of this are just guesstimates by me, as this would be the intial route I would think to try, If I HAD to do this. But lol, I wish you the BEST of luck since what you are doing is the reverse of what I normally do and you're doing it blind (no lens data and no camera position info)

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