I think you'd get enough votes if the app was in the right format. It would have to be like hot or not, where you have 2 photos, pick one, and instantly get another 2 photos along with the results from the first set. This gets people trapped in the just one more click mindset.
Focus it on fashion and clothing, people will vote to see more photos, to judge the outfits of others (a lot of people enjoy doing this for fun), and to get inspiration for themselves.
Also, allow users to select what gender and age groups can vote on their photo.