"I have a photo from that day" — adding to someone else's memory
Under any memory, people on the page add what they remember — a signed note, with photos of their own. The photos stay with the note.
Under a memory, What others remember is where the people on the page add their side — a few lines, and any photos they have from that day. Each note is signed, and it's the only way to add to someone else's memory: the memory's own photos stay the author's.
The photos stay with the note
A photo you add here belongs to your note: it's reviewed with it, shown with it, and goes if the note goes. It doesn't join the author's carousel. A note can even be photos only — Dave added 2 photos.
Switches
The author can turn notes off for one memory (Allow notes on this memory), and a manager can turn them off for the whole page. Off hides the notes; nothing is deleted.
Notes are not comments: they're for what you remember of that day. A response that isn't a memory is a gesture. See Gestures.