What's the difference here between adding the "custom pass" and just taking a photo of QR code? Just the fact that it is stored in Wallet instead of photos folder?
In addition to the sibling comment: I really dislike opening my Photos app in front of other people.
It's stored in Wallet so you can access it through the Wallet shortcut (double-press power button), when you open it the screen automatically brightens, and it's a perfectly clear QR code rather than a picture so it'll be easier to scan.