Just be careful where you store your digital photos - I just lost years worth of digitalized photos because the internet company was bought out and I missed the email (due to change of address) to retrieve my photos by just a couple of months.

Another thought - my uncle, an avid photographer, used onion skin paper (very very thin) as an overlay, then labeled the people on it on top of their position.

Depends on the age of the photo, but I had some old ones (~70 yrs) that were mounted on heavier paper, so pencil lead or even pen ink wouldn't bleed through. Unfortunately they were lost in a flood.