I'd probably see the website as a third entity presenting stuff to me, so it's coming down to: Your = "I'm presenting you your photos which i just store for yo

I'd probably see the website as a third entity presenting stuff to me, so it's coming down to: Your = "I'm presenting you your photos which i just store for your convenience". My = "You've uploaded your private photos, now they are mine, dumbass!" Definitely "Your", in my oppinion.