The photo was published simultaneously in many newspapers, some of which had no copyright notice at all (neither for the photo in particular, nor for the newspaper as a whole). For example:
Also published without copyright notice in (1976) The Instant It Happened, H.N. Abrams & The Associated Press, p. 211 . (The book contained only an "All Rights Reserved" notice, which is not a valid copyright notice under US law.)
Copyright was therefore forfeited per section 9 of the Copyright Act of 1909, which required that notice of copyright be affixed to every published copy.