The Hidden album can keep selected photos out of the main library. On current iOS versions it can also be protected by Face ID, Touch ID, or the device passcode.
- Open the Photos app.
- Scroll to the utilities or collections area that contains Hidden.
- Tap Hidden and authenticate if requested.
- Open a photo if you want to view it or use the available controls to unhide it.
If the Hidden album itself is not visible, check the Photos settings for the option that controls whether the Hidden album is shown. Hiding a photo is organizational privacy, not a separate encrypted vault.