The GDC has probably been trying to figure out how to sneak a RickRoll into a game hint for several years now. I'm not an expert, so I can't tell if the RickRoll was edited into a photo taken from a phone or if the RickRoll was printed, tacked up, then taken as a photo from a phone (as implied).
fotoforensics
The RickRoll ELA is a darker image than the surrounding image. However, given that we don't have enough comparative surface of solid colors, nothing's conclusive -- the white paper obscures the ELA of the RickRoll photo edge. The fact that all pushpins are totally obscured in the ELA is interesting, but I don't know enough about it to draw a hypothesis as to why. Assuming the bottom left pin is flat, all of the shadows line up. Given the GDC's history of adding fluff to hints, I'm going to presume the flat pin simply means the person who tacked up the photo only had 3 non-flat pushpins (i.e. don't look into it too much). The jpeg quality (90%) implies that the photo was saved twice (once when taken, once after -- probably a crop), but that's subject to the default jpeg quality of a HTC Evo 4g.
So -- nothing conclusive, but the GDC should beware that the internet provides many resources to figure out their schemes
FYI, the guy who made Fotoforensics also writes a blog I read weekly (you know, while code compiles...).
http://www.hackerfactor.com/blog/
Some very interesting articles about photo manipulation there.