Concept:

Pen pals, but instead of sending letters you send an undeveloped film roll or disposable camera.

Because a picture is worth a thousand words right? And you kinda share/give away the experience of seeing your pictures for the first time. (Of course they share the scans with you after developing)

You could define topics or themes beforehand or the pictures can be about anything you want, just sharing things you like… I don’t know, just a thought…