MLA
Howe, F. L. Greetings from Picturesque America : Who's a Nigger : Two African American Boys Fist Fighting and Several Surrounding Them Watching : a Woman with a Bald Eagle, a Scroll and American Flag. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 73. https://digital.library.emory.edu/purl/941zcrjdjb-cor.
APA, 6th edition
Howe, F. L. Greetings from picturesque America : who's a nigger : two African American boys fist fighting and several surrounding them watching : a woman with a bald eagle, a scroll and American flag (Box 73) [Postcards]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/941zcrjdjb-cor.
Chicago
Howe, F. L. “Greetings from Picturesque America : Who's a Nigger : Two African American Boys Fist Fighting and Several Surrounding Them Watching : a Woman with a Bald Eagle, a Scroll and American Flag.” Postcards. Robert Langmuir African American Photograph Collection, n.d. Box 73. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/941zcrjdjb-cor.