it is because you are logged in to view them as say user1, but to alter them you need to have permissions, so user2 could have permissions e.g. read, write etc.
so depending on the permissions of a user depends if they can upload or not.
Spammers next time you spam me consider the implications:
(1) that you will be persuaded by me(in a legitimate mannor)
(2)It is worthless to you, when i have finished