Not always. The only way to get the sharingan if you are not an Uchiha is to have a medical ninja transplant his sharingan eye into their own. I would say he is not an Uchiha because an Uchiha would have a sharingan eye in both eyes, while Kakashi and Danzo only have one Sharingan eye.
He is not an Uchia he took an uchia's eye that is very powerful especially with powers of persuasion. He also has many sharingan eyes on his right arm (i think ten) and the first hokages cells in him so he can use izinagi (not sure how to spell that name might be wrong) which alows him to make any wound or death a dream. In other words he can make it so he was never hurt. (he can't fully do it though but Tobi who is actually madara can use it well-for five minutes. danzo can only use it for one minute).
It is Uchiha Shisui's who is the guy that Itachi killed to get the last form of the sharingan.
There are only a few known Naruto characters that posses the Sharingan. The first is Uchiha Madara. He and his brother Izuna are the first of the uchiha to obtain the Mangekyou Sharingan. The Second and third is Uchiha Itachi & Uchiha Sasuke. Next is Uchiha Obito. He gained his sharingan while on a mission with the soon-to-be Yondaime Hokage, 13 year old Kakashi and Rin but died shortly after. Kakashi and Danzo are the only known Non-Uchiha Sharingan users. Kakashi got is from Obito and Danzo stole it from the murdered Uchiha Shisui. Lastly is Uchiha Shisiu. Not much is known about him but it is common knowledge that he was murdered by Itachi to gain the Mangekyou.
Danzo gets Sharingan by killing Uchiha and taking their eyes
no one knows but if he is obito uchiha then you should know
For those who are alive until shippuden it is Kakashi- Madara Uchiha- Sasuke Uchiha- Itachi Uchiha- Danzo
Sasuke Uchiha, Tobi AKA Obito Uchiha, Madara Uchiha, Shisui Uchiha, Kakashi Hatake, Danzo and Itachi Uchiha.
Sharingan can be implanted into people who are not members of the Uchiha clan. Kakashi is one example, Danzo is another.
behind Danzo's mask is what Danzo absorbed out of Uchiha Shisui.
Well, Danzo can have sharingan by having absorbed uchiha shisui's color into his right side of the body. Obito did this to Kakashi when his eye was badly damaged. He put one sharingan eye into his damaged eye. Since Kakashi is not a member of the Uchiha clan, he cannot deactivate his sharingan eye. Because of this, he usually keeps it covered with his mask to conserve chakra.
There is no sixth hokage. Danzo was a candidate for it, but was killed by Sasuke before he could formally take over, and Tsunade recovered in the meantime. Danzo is not Madara, he is not even a Uchiha. His sharingan eye was taken from Shisui Uchiha.
He Got it From Obito when he was on a mission when he was younger. Obito got crushed by a rock and gave kakashi his Sharingan as a gift before he died. Obito had the Sharingan because he was an Uchiha.
the "Naruto" carachters that are capable of using the mangekyou sharingan are Sasuke Uchiha, his brother Itachi Uchiha, Madara Uchiha (Tobi in the Akatsuki Organization) and, in the past, his brother Izuna Uchiha. and, even though he is not part of the Uchiha clan, Kakashi Hatake, who received it from Obito Uchiha.