The order the images are in is the order of the numbers you found
There's should be one in one of the girl's bathroom stalls, the other is a photo in a classroom that you have to tape up, (you need a tape item from one of the lockers) and the final one is in the Nurse's office when you use the charcoal on one of the posters
But if you just need the code then (Spoilers):
57409