If you look at the knees and shoulders you will see that they are not the same person duplicated over and over. You can also see changes in the lighting on the individual people. IMO, it looks like 27 people in full body stockings that have the markings printed on them. OR, 1 photograph of each person, 27 total, then multi-printed on one sheet of paper, this would require a very, very skilled darkroom printer to make this look as good as it does, lots of very precise masking. There are of course other possibilities.