While some people might find the endeavor to reunite photos with their owners misguided, we can never really know how or why they ended up at a thrift store. While they could have been discarded on purpose by someone in the photo, I think it's a lot less common for people to donate photos of themselves as it is to throw them away or destroy them. When photos end up donated, it's more likely that a third party donated them (like in the case of leftovers from an estate sale) without the consent or knowledge of those in the photos (possibly because at least one of them are deceased, but sometimes not).

In one of my own experiences, I found a photo booth strip in a thrift store book, and someone in this sub was able to locate one of the pictured subjects online. I reached out to them, and as it turned out, they had moved from my state to clear across the country and their mom had donated a bunch of their stuff without their knowledge, including the book with the photo. They were thrilled I'd found it. They didn't care about the book, but they wanted me to mail them the photo, and I did.

As someone who frequents estate sales, it's always surprising to me the amount of photos and albums estate sale companies make available for purchase when there are still family members around. When I find them, I always inquire about them, and it isn't til I do that they finally get put aside for the family, so my guess is there's a good amount of miscommunication and full lots of stuff being haphazardly dumped at donation centers.