visitator can whatch album but no photos. how?

Hi,
i want to make a prticolar permission: visitator can whatch album and so also the previw of photo in album, but can whatch image page by clicckkin on the image in album, in this chance gallery show an error message that say: "you mast register to view image page".

Or when visitator try to acces on the image page, they can visualizze a very smaller image whith error message that say the same: you mast register.

Thanks