MLA

Whitman, Walt, 1819-1892. G[ustav?] Kruell woodcut. Box 4, folder 190. n.d.. https://collections.library.yale.edu/catalog/2053819.

APA, 6th edition

Whitman, Walt, 1819-1892. (["Box 4, folder 190"])(n.d.)[G[ustav?] Kruell woodcut]. https://collections.library.yale.edu/catalog/2053819.