Copyright on Photos when the photographer and subject is dead

I have hundreds of vintage photos dating back to the 1800s some are as late as the 1960s. I purchased most of them from antique stores and different shows.

I now want to use them in artwork that I will be selling.

I know that the photographer owns the copyright. But these photos are between 60 and over 100 years old. In most of the photos, the photographer, and even the subjects died long ago.

Most of them don’t have any names on them at all. They are just personal snapshots. There are some more formal portraits . Some of them do have the name of a photographer or photography studio.

I’m just wondering if I use one of the photos and someone pops up and says oh that’s my grandmother I recognize her… Then what?

Does anyone have any ideas how I could find out the answer to this question