A free app for Android, by mallow.

Hide Pictures Gallery Vault is the best way to protect your photos from intruders and nosy friends and family members. The app hides pictures and videos by encrypting them with a PIN, pattern, or fingerprint and then stores the secure files in a separate gallery vault. You can even create multiple gallery vaults and encrypt your photos and videos within a vault.

When you install the app, it will ask you to set a PIN, pattern, or fingerprint. Once you set the password, the app will start hiding your photos and videos. To view your files, you must enter the correct PIN, pattern, or fingerprint.