This photo is frequently mistaken as a picture of Homer Plessy. It is actually Pinckney Benton Stewart Pinchback (10 May 1837 - 21 December 1921), former governor of Louisiana. The photo was taken by Matthew Brady and is housed at the Library of Congress.
Homer Plessy was a "Creole" who was 7/8 white and 1/8 black. In deciding whether Mr. Plessy could be subjected to the indignities of segregated travel, the Supreme Court of the United States found that “separate but equal” was not a violation of constitutional law.
Plessy v Ferguson (decided in 1886) remained the law in America for decades - until a 1946 case, called Morgan v Virginia, reached the Supreme Court.
In that matter, the Court found that states could not require segregated transportation when the mode of travel crossed state lines:
As no state law can reach beyond its own border nor bar transportation of passengers across its boundaries, diverse seating requirements for the races in interstate journeys result. As there is no federal act dealing with the separation of races in interstate transportation, we must decide the validity of this Virginia statute on the challenge that it interferes with commerce, as a matter of balance between the exercise of the local police power and the need for national uniformity in the regulations for interstate travel. It seems clear to us that seating arrangements for the different races in interstate motor travel require a single, uniform rule to promote and protect national travel. Consequently, we hold the Virginia statute in controversy invalid.
Even though the court’s ruling was helpful (in a theoretical sense), it had no meaningful impact. Since the Justices did not find all segregated transportation to be unconstitutional, various states could still allow segregated transportation within their own borders.
Forcing people of color to sit in the back of railroad cars, buses and other forms of travel did not end until the Civil Rights Movement of the 1960s.
Photo of Pinckney Benton Stewart Pinchback by Matthew Brady, online courtesy Library of Congress.