How do guests find their photos with a selfie?

Guests take a selfie and see the photos they're in. It all happens on their own phone: nothing about anyone's face is uploaded or stored.

What guests do

They tap Find my photos in the gallery's row of tabs: first on a phone, at the far end on a computer.
A short note tells them their selfie stays on their device. They tap Take a selfie, or Choose a photo of just them.
The gallery looks through every photo, counting as it goes, and the photos they're in appear as they're found, surest first. Stop ends it early.
They tap a photo to open it, or Add them to my favorites to keep them all. As with any first favourite, they're asked for their name and email.

Open the gallery's Settings › Access.
Untick Let guests find their photos with a selfie. It's ticked in every gallery to begin with.

A guest can't see Find my photos: Check that the gallery has at least 20 photos, and that Let guests find their photos with a selfie is ticked. On a very old phone or browser, the gallery says it can't look through the photos.
A guest says a photo of them is missing: A clearer selfie helps: good light, looking straight at the camera. They can always open the photo in the gallery and tap ♡.