MLA

Stieglitz, Alfred, 1864-1946. Cabinet card portrait with Louis Schubart and Joseph Obermeyer, by Loescher & Petsch, Berlin. Box 133, folder 2540. [1887]. https://collections.library.yale.edu/catalog/17357457.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 133, folder 2540"])([1887])[Cabinet card portrait with Louis Schubart and Joseph Obermeyer, by Loescher & Petsch, Berlin]. https://collections.library.yale.edu/catalog/17357457.