My grandmothers wrote names of a few friends on the backs of hers - I have created a small family tree for these people at Ancestry, added the photos, and if someone else copies them to their tree, I'll be able to remove those disconnected branches from my tree. Others I've been uploading to Google Photos where I can write what I know about them, then send a link to the album to DNA matches or more distant cousins. They have then forwarded links to other family and I have had several IDs and some guesses confirmed or refuted. I am now a member of the Facebook group - Genealogy -Dating old Photographs. The generous expertise of some of the members there who know cars, architecture, hairstyles, clothing, shoes etc, in addition to some who know a lot about the photography printing styles or styles of studio portraits is helpful to placing names on people.