Just for grins, here are the only two photos I know of, from November 25, 1920, when Jack Johnson boxed two matches in Leavenworth prison. I believe the first photo shows him fighting 'Topeka Jack' Johnson, with his other opponent (Frank Owens) standing to the right. The photo to the right shows him with Owens as well. But I could have Topeka Jack and Owen switched
Johnson fought Owens first, and beat him up badly, so it doesn't make sense that he would be standing around for the other fight. According to the papers, Owens weighed 227 pounds, and Topeka Jack Johnson weighed 210.
(This occurred Thanksgiving Day, 1920, whereas the postcard images were taken 13 years earlier).
Topeka Jack Johnson, whose name, wrote Mark Ribowsky in "A Complete History of the Negro Leagues, 1884 to 1955," "wasn't Jack Johnson at all until he stole it from the mountainous black prizefighter who won the heavyweight title on the day after Christmas in 1908."
Topeka Jack was a prizefighter, too, albeit one of limited success in the ring. The two Johnsons also knew each other, as Topeka Jack was described by the Leavenworth Times in a Nov. 25, 1920, story as a former sparring partner of the champ.