The heart never shows a number to the room. It tells the host, quietly, which photos landed.
Liking
Tap the heart on a tile (on a desktop, it appears on hover) or in the photo viewer. Tap again to unlike. Guests who aren't signed in are asked to confirm an email first (the same free account as everything else), because a like is tied to a person.
Every photo you've liked, on any event, collects under Likes on your dashboard, newest first. Unliking there drops it from the list.
What the host sees
On the host's view of the gallery, a photo with likes carries a small badge with the count. That badge is host-only: guests never see totals, so nobody's photo gets publicly ranked. It's the room voting, privately, for the host's benefit.
What likes feed
Your own shortlist. Liking as you scroll is a fast way to mark keepers, and Select then Like marks a batch at once.
What they don't do
There's no "sort by likes" on the album yet, for hosts or guests; the gallery is always newest first. Likes don't affect what's shown, hidden, or approved, they don't change what the highlight reel plays (it mixes every photo guests can see, afresh each loop), and they aren't visible on a public profile.
Tell the room to heart things
A line in the announcement ("heart your favorites") turns the heart into the crowd's vote, so the morning after you know exactly which shots landed, and which to put in a clip of your own.