Even so...
Danzo's abilities were very limited with the sharingan on his arm, he was able to use Izanagi because he had attained both Uchiha and Senju DNA (probably by working with Orochimaru), the sharingan on his body could not physically "see" but they could potentially be used to a significant extent as shown by Danzo himself...
As for Tobi's sharingan, the one in his right eye socket is probably and most likely Obito's, since whenever he warps his whole body away, it is centralized around his right sharingan...