I have recently seen something done like this from pictures.
(1) blow the picture up to the size you want
(2) take teracing paper or a thin paper and lay it over the picture
(3) draw a grid of squares off on this paper
(4) remove the paper and lay beside the pictures and then label or color with color pencils the colors each square should be
(5) replace the paper on top of the print and begin piecing from the grid using the colors you choose
I hope this makes sense.