Film production expert Eve Light Honathaner says in The Complete Film Production Handbook (Focal Press, 2001 p. 211.):

"Publicity photos have traditionally not been copyrighted. Since they are disseminated to the public, they are generally considered public domain, and therefore clearance by the studio that produced them is not necessary."

Film industry author Gerald Mast, in Film Study and the Copyright Law (1989) p. 87, writes:

"According to the old copyright act, such production stills were not automatically copyrighted as part of the film and required separate copyrights as photographic stills. The new copyright act similarly excludes the production still from automatic copyright but gives the film's copyright owner a five-year period in which to copyright the stills. Most studios have never bothered to copyright these stills because they were happy to see them pass into the public domain, to be used by as many people in as many publications as possible."