The technique of blocking some parts of a photograph to emphasize (or draw attention to) another part of the same photograph is called

framing, i believe that is what it is called

romare bearden worked with many types of media which includes cartoons, oils and collages. basically, the use of collage him create emotionally affecting images hence back then he had struggled with his two artistic sides as a student of literature and of artistic traditions and being a black human being which involves very real experiences, fugrative and concrete.thus through the use of collage expressed or showed how his art/work became more representational and more overtly socially concious. he showed how not only were african-american rights moving forward but so was his socially concious art and by then his works became generally considered as best works in 1964.