Who owns the copyright on a vintage amateur photo print?

Who owns the copyright on a vintage amateur print, if you own the only copy of the print, ie you now have the master copy/only copy in existence and the photographer was an amateur who died many many decades ago.

I collect old prints from estate sales and thrift shops, some of them are really nice and I've often wondered how the copyright on these images would work if I decided to sell reprints of them.

I can appreciate if it turned out the photographer of a print was well known and their estate is enforcing their copyright then this is a moot discussion but theoretically if the copyright owner of an image was deceased and no one was enforcing the copyright ownership?

Also another scenario is copyright protection lasts for the life of the author plus an additional 70 years. If I have the only copy in existence of an image and the authors copyright protection has now lapsed who would own the rights to profit from the reprints of that image and would anyone legally be allowed to scan those reprints and sell them themselves?