I think DeCarava was considered a "Master of Photography" because around the time when he started to photograph, he was able to document the Harlem Renaissance and photograph all prominent Blacks in the community. He also captured the everyday life of the Harlem residents and give a peek into the culture.
Parks was considered a "Master of Photography" because as journalist and a employee of Life Magazine he was able to participate in social movements through his photography. He was allowed to document peoples lives that were apart of the struggle.
Ralph Meatyard, Lucybelle Crater and close friend Lucybelle Crater in the grape arbor (from "The Family Album of Lucybelle Crater"), 1970
I think Meatyard is considered a "Master of Photography" because he was a photographer that photographed is family and friends. He wasn't your usual photographer out to take pictures of a movement, he staged photo's and used props. He was a pioneer and ahead of his time.
My personal pictures