I've also got quite a lot of unknown people in photographs - I asked my Mum when she was stuck for something to do, to put all the huge drawer of photos she had into albums I provided, and caption them ... bless her, she proudly showed me the first full album - all labelled with my name and various ages! And I'd thought she knew who I was!
We actually chuckled about it, she'd not realised I didn't know who all these people were. Sadly she couldn't recall who most were with any clarity, especialy not those from my father's side.
It'll be a lot harder for future generations - loads of "Kodachrome" slides my parents took are mere ghosts of their former selves. I spent days scanning and downloading them, but can imagine that in future generations all our on computer images will be not only impossible to identify, but probably impossible to access/ retrieve.