How long does a photo copyright last?

I ran across some vintage Shelby County Photos that I wanted to post on this web site.  The photos appear to be between 1900 to 1970?   Unfortunately, I have know idea who the photographers were in order to determine if the photos ever sold.

According to the library of congress.

"the term of copyright for a particular work depends on several factors, including whether it has been published, and, if so, the date of first publication. As a general rule, for works created after January 1, 1978, copyright protection lasts for the life of the author plus an additional 70 years. For an anonymous work, a pseudonymous work, or a work made for hire, the copyright endures for a term of 95 years from the year of its first publication or a term of 120 years from the year of its creation, whichever expires first. For works first published prior to 1978, the term will vary depending on several factors. To determine the length of copyright protection for a particular work, consult chapter 3 of the Copyright Act (title 17 of the United States Code). More information on the term of copyright can be found in Circular 15a, Duration of Copyright, and Circular 1, Copyright Basics. "

Staying legal.

Even though I have several photos of this time period in my personal collection,  I can not upload them until I can confirm that they are no longer under copyright.

Postcards.

Most of the cards in my collection have the publisher of the card.  Also, most have been mailed so there are postmarks that gives me a timeline.