Just because it's already been stolen on other websites, that doesn't justify replicating it further.
I don't know if it is of any interest to you, so I'll go ahead and tell me if you're not into philosophy, but Kant's autonomy says exactly that. You are only responsible for your actions, and not those of others, but in turn, other's actions do not alleviate your own actions. If a thousand people stole a photo, It'a a thousand times the same crime, not one crime and 900 lesser crimes. :)