Thinking back about Tobi's battle with Konan, he used Izanagi to escape from Konan's ultimate technique! I searched through blogs and Narutopedia but couldn't get the source of his left eye, that he used to overcome Konan's ultimate technique.
So here we have to look at Tobi's left eye. The one he used for izagani. I researched a bit into it and looked into Sharingan user eyes since it struck me as very familiar. I realized Madara's EMS looked very similar to it, and I decided to look up his brother's eyes since EMS is a combination. The bottom picture of the Sharingan eye is Madara's brother, Izuna Uchiha, eye. Taken that Madara saved Obito/Tobi, I believe that when Madara died, he took his eyes. However this is a theory, but the eyes are very similar.