The registration email, before anyone arrives
A conference, festival, or concert has a list of people who already said yes. Put the frame link in the confirmation email next to the calendar file and the venue map. Attendees who set the picture before travel are doing your marketing in every group chat they already belong to. That is different from a birthday, where the list is a family thread and the window is one day.
If tickets are still on sale, the framed photos are social proof that the room is filling. The counter is people who bothered to save an image, which is a colder number than “interested” clicks on a Facebook event.
