Why ask for this? We were asked for Hallowe'enish/Creepy screenshots also, and many participated on Facebook.
You don't even give a small prize to those who participate. It's nice to see the pictures, but you could atleast make a little event out of it.
Just don't get why you ask this of the players, when you don't reward them for their troubles (and in a way, promoting your game by sharing their stuff here and on facebook). You don't seem to care about individual class stories or companion stories, or extending them, the way they deserve to be, so why ask for pictures of our 'Saga moments'?
it's their way of "interacting" with the community