Final answer:
Matthew Brady was the first documentary photographer of the Civil War. Dorothea Lange captured the plight during the Great Depression. Lewis Hine documented child labor by often disguising his identity.
Step-by-step explanation:
Matthew Brady is best described as the first documentary photographer who captured the Civil War in pictures. He used a portable darkroom to develop glass plates on the spot, capturing the aftermath of battles rather than the battles themselves due to long exposure times. His work, such as the 'The Dead of Antietam,' exhibited in his New York gallery, brought the harsh realities of war to the public, earning him the nickname the 'Father of modern photojournalism.'
The documentary photographer who photographed the conditions of Americans during the Great Depression is Dorothea Lange. Her iconic image 'Migrant Mother' is one of the many powerful photographs she took while traveling the Dust Bowl states, documenting the severe impact of the Great Depression on farmers and migrant workers. Lange's work was part of a New Deal program wherein photographers were employed to document social conditions.
Lewis Hine was the documentary photographer who would often misrepresent himself to gain access into factories to photograph the harsh realities of child laborers. Working for the National Child Labor Committee, Hine used photography as a tool of realistic documentation to bring attention to social issues, including the dire working and living conditions of children.