Yeah, but you can't force people. If you've any ideas to spice it up a bit and get more people involved feel free to post them up.
I was thinking of allowing people to post more than one picture...but then they might have votes spread over a number of photos and not have one with the most votes...if you get what I mean.
Maybe allow people to post a selection early on, but have to pick a 'final' photo for the vote - maybe this would stimulate more photography discussion?