I just finished a unit on the self-portrait and had middle school students create grid self-portraits. We xeroxed their original photos then they had to measure and draw a 1/4 inch grid directly on the xerox. They next drew a one inch grid on larger drawing paper and enlarged the smaller image step-by-step. I know this approach takes longer but I think it is worth it - the students definitely needed the measurement skills and their final works were really great. Instead of xeroxing photos, another approach is to photograph the students with a digital camera and print them.