An idea articulated by Douglas Hofstadter in I Am a Strange Loop may cast some light on this. Hofstadter suggests that each human "I" is distributed over numerous brains rather than being limited to just one brain -- that is, a human identity is a phenomenon of relationships between people, not something that exists on its own.
An analogy could be made with the nature of a secret. As has been pointed out, a secret is not (as we may tend to think) something that exists within a person's head, but rather a relationship between two people. 
And so with some old photographs. The people to whom they were significant, precious are now themselves dead and so are those who knew them. The network, the circles of relationship are broken forgotten faded.