Horace Traubel, when he got the photo from Whitman, had trouble identifying the photographer too, speculating that it was a Sarony, but that seems unlikely.
For more information on Mathew Brady, see "Notes on Whitman's Photographers."
Photographer: Brady, Mathew B., 1823–1896
Date: ca. early 1870s
Technique: photograph
Subject: Whitman, Walt, 1819-1892
Creator of master digital image: Whitman Archive Staff
Rights: Public Domain. This image may be reproduced without permission.
Work Type: digital image
Date: ca. 1995–ca. 2000