if you were going to use the pictures as part of an ad to sell peanut butter you might run into model release issues if the people, or their heirs, recognized them and said "why is uncle filmore on this jar of peanut butter?"
But if you just want to post them on apug, or facebook, or any other social media or photo web site, that comes under journalistic fair use, just like the newspaper: Look at these images I found, fun, huh? you're not using them commercially, you're just showing them to folks. It's your little bit of the First Amendment.
Some artists use images like that for art collages, and they find their source material at yard sales and thrift stores. Same rules apply to you as them --
so go ahead and show. No problem. They're your pictures, you just don't own commercial use of the images of those people.
c trentelman, journalist.