I dont want to comment specifically about this website as officially i'm absolutely nothing to do with it, dont want to sound like i'm making myself out to be a part of it when i'm not.
But, i THINK there is something on the back of match tickets or in small print somewhere inside the ground saying that photographers are present and by being there you give your consent to be in the photographs. I remember Man Utd fans kicking up fuss about being in a nike advert without consent and nike got away with it because they had wee signs down the front of the stand saying something along the lines of "Nike Advert filming in progress, if you object to being filmed please leave the premesis".