Open the Photos app
Select the photo or video you want to lock
Tap the Share button
Tap Hide
Confirm by tapping Hide Photo
Open Settings
Tap Photos
Turn on Use Face ID or Use Touch ID
Turn on Hidden Album
Open the Photos app
Tap Albums
Scroll to Utilities
Open Hidden
Authenticate with Face ID, Touch ID, or passcode
For stronger protection, move sensitive photos to a locked notes app or a third-party vault app
In a third-party vault app, import the photos and enable its passcode, Face ID, or Touch ID lock