My guess is it being Cathy doesn't matter. The point wasn't to fuck Cathy over, but the DIKs, imo. It could've been any teacher, and the perpetrators just chose Cathy. It could've also simply been convenience, if they stole the photo. Swipe a whole bunch of shit, peruse through it, and see whats usable. That sort of thing.
Its no coincidence this happened on the heels of the Jocks photo shenanigans. If it was just about Cathy, there'd be no need to go through the extra effort of posting it through the DIK account. Just make a fake account, tag the right people for exposure, job done.