The first time you visit Montsaye High (The very first level) after
freeing the ghosts. After the cut scene with Hawksmoor and Anna in the
attic, buyt before YOU go there. In one of the classrooms, it is a
science-ish room. On a table near the window is a TV and a slide
projector. Go up to the projector and an option for action appears.
(Push, or activate or something) Press this button to see a mysterious
shadowy figure. Press it again to see another image. Keep on doing this
until you come back to the original slide.