I found that even if I trim the edges perfect, 
the cel will look different with the DVD 
captioned background, simply because one has been 
filmed and one is the original, and the cel will 
always look more crisp and vibrant than the 
background. So, like you said, great effort but 
doesn't work this way. I guess the best way is to 
get the original background, or to get a colored 
copy. Anyway, I gave up, I think they look good 
enough with the white backing boards.