(image copyright Morgana Ryan)
Mosaic of a donkey from Tunisia. Here you can see the style from that region where the tesserae for the figure are smaller than those used for the background. So long as the size difference isn't too great you can get away with it. The thing to watch out for is not using larger tesserae for the background just because it's quicker.
'If you want to know how much care has been taken over a copy then look at the background first.'