Wants to Use Historical Photos in Book

Dear Rich, I have photos I want to use for a book I am writing. The photos were given to me by the photographers. As far as I know these photographs were never published. They photos were taken in various years including 1914, 1924, and 1965. The photographers are all now deceased. However, the people who gave me the photos were informed that I was writing a book about local history and were going to use the photos for research. Can I use these photos in my book? Do I need to try to contact the descendants of the photographers in order to get permission or can I just credit the source of the photographs? I also want to use a photo I found in a history book. The photo is a pre 1923 portrait of a local man. The caption for the photo reads “Courtesy of William B. Secrest, Fresno, California.” Secrest is the author of the book and owns the original photograph. Do I need to track down William Secrest or can I use the photo without permission since it is pre 1923? The history book was published in 2002. I would of course appropriately cite the photograph. We think you'll be okay to use all of the photos described, but it gets a little complicated.
The 1914, 1924, and 1965 photos. If the photos were never published and the photographers died before 1941, the works are in the public domain (Here's the official explanation). Otherwise, the unpublished photos will not become public domain until the author has been dead for 70 years. (Based on this rule, the 1965 photo could not be in the public domain.) Even though your one or more of your uses is likely to be unauthorized -- and an infringement --  we think that you will have a strong fair use argument, and we also think that the likelihood that the descendants of the photographer will learn of your use (or care) is slim. A commercial publisher may require that you indemnify the publisher if there is a problem. You may want to consult an attorney at that point.
As for the pre-1923 portrait. If the pre-1923 portrait was first published with authorization before 1923 it's in the public domain and you're free to use it. If it was first published after 1922 but before 1964, the photo is in the public domain if it wasn't renewed (and most were not). If the first publication was in 2002, and the author died before 1941, it is also in the public domain. (See, we told you it was complicated). As for the prolific California historian William B. Secrest, we think -- and we could be wrong -- that he owns the photo and lent it for use in the book. The "courtesy" he has extended is that he provided access to the photographic print. Was there a copyright notice associated with the publication in the 2002 book? That could also be indicative, though not decisive as to the photo's copyright status.