Yeah behind that scenes bungie is using that mask to reveal parts of the hidden message - the hidden message get's buried into the left image as a blur using a forward Fourier transform. The automation process just undoes that fourier transform every 5 minutes and adds the new pieces revealed by the geomask to the image in the dropbox link. But the geomask is directly affected by how many people are on - what their location is * by a timing function. So by logging into a node everyone reveals the secret image.