I have a photograph of my great-great-grandparents taken around 1900 on the front porch of their home with all their children. The individuals are all identified in a reprint of the photograph that was done in the family genealogy published in 1986. I’m fortunate to know who they are.
But I’m not certain exactly how I came to have the photograph. I have documented how other items came into my possession, but I’ve realized that I have things whose acquisition I’ve not documented sufficiently. The easiest way to document acquisition is to keep the items organized by how and when they were obtained and notate where you received them from.
That “how you got it” is especially important for photographs that are unidentified.