Yes, this is Barack Obama. It is a photo by Lisa Jack, taken in 1980 at Occidental College. (From Lisa Jack's artist statement.) The work was exhibited at M+B Gallery in West Hollywood, among other places.
He has been known to smoke pot: "I inhaled, frequently. That was the point."
I can find no evidence in any text online that the claim is true. (This does not prove that it is false, though.)
The first online reference that I could find to "Barack Oganja" as an early nickname for Barack Obama is on May 18, 2012:
- https://www.facebook.com/fact5/posts/366700466713262
- https://twitter.com/FactBoook/status/203585034484068352
This is consistent with Google Trends not showing any activity for this term before June 2012.
One individual created this nickname for themself prior to 2012.
One user attributed a Barack Obama quote to "Barack Oganja" on December 4, 2011, but didn't claim it was a nickname from his younger years.
Two marijuana growers named a strain of marijuana "Barack Oganja" (reported December 4, 2009)
One blog called Barack Obama "Barack O-Ganja" in a headline on October 26, 2009, but didn't connect it to a nickname from Obama's earlier years.