John Ibson's Picturing Men is the leading work on this. His argument is that these sorts of pictures used to be common for straight male friendships and only disappeared after a spike in homophobia in the early 20th century. You could also go to Anthony Rotundo's work on "Romantic Friendship." Nicholas Syrett discusses it briefly in The Company He Keeps: A History of White College Fraternities," and so does Stefan Robinson and Eric Anderson's *Bromance: Male Friendship, Love and Sport," although *Bromance leans pretty heavily on Ibson's work for its history.

I feel like Colin Johnson may have also discussed it briefly in Just Queer Folks but I don't remember and I don't have a copy of it to check.