There's a fad that has been going around for at least 15 years. I
recently saw it in a fitness (running) magazine. Polaroid negatives that have
been printed and blue toned or sepia toned after the printing. The leftover
from the pulled negative are the ragged borders of the print. You might try
to have them do this on photoshop by changing the colors. Have your students
also gang the small prints onto a larger print in a pleasing matter leaving
those ragged edges showing.