You can hide sensitive images from your Photos app’s Camera Roll by moving them to the app’s Hidden album, but it doesn’t take much for someone with access to your handset to find the Hidden album and start perusing through the images it contains.
With this caveat in mind, iOS developer Menuska has released a new free jailbreak tweak called FaceID for Hidden Photos that adds a biometric authentication requirement to the Photos app’s Hidden album. With it, you’ll need to pass a Face ID authentication test to access the Hidden album’s contents, as shown in the screenshot example below: