One common issue is the images alone are rarely sufficient to tell a story, so you need to collect their context before the owner is gone.

One interesting bit is generalisable knowledge can be inferred from old pictures, but that'd be mostly relevant for specific events, or very old pictures.

Although I guess vacation pictures from e.g. the post-war period could be useful for ecological studies, if their location is known. Things like indoor christmas pictures, less so, even though from an emotional perspective they were undoubtedly dear to whoever took them.