Do my guests really not need to install anything to see their photos?

Correct — no app, no software, nothing to install. Guests just open a link you share, or point their phone camera at a QR code you've printed and placed at the venue. That takes them to a simple web page where they register once (name plus an email or phone number) and upload a selfie. A minute later they're looking at their own private little gallery. Keeping it app-free is honestly one of the smartest things about it, because asking eighty wedding guests to download an app is a losing battle.