The picture was shot by Milton McFarland Painter Sr., an amateur photographer who lived in the Delta. It was likely made while Brewer was governor, but the picture carries no exact date.
As governor Brewer did a variety of early-20th century progressivey type things, such as creating a Bureau of Vital Statistics, regulating bank interest rates and strengthening child labor laws.
He appears to have been at least somewhat progressive on race, especially for someone who's daddy was a plantation overseer and a captain in the Confederate army. After his term as governor, Brewer returned to his law practice. In 1936 he argued and won a case before the U.S. Supreme Court on behalf of three black Mississippi men who had been convicted of murder solely on the basis of their confessions. The three men had confessed -- after being brutally whipped.
The Supreme Court threw out the convictions, ruling that a confession "extracted by police violence cannot be entered as evidence and violates the Due Process Clause of the Fourteenth Amendment." (Wikipedia)
The case is seen as one of several key rulings establising the rights of the accused leading to Miranda in 1966.
As for the badass part, I mean, c'mon, just look at him.