A free app for Android, by Raamo Apps.

Photo Lock-Hide Photos Videos is a secure, private photo vault. Hide your photos, videos, and other files with a simple import and secure your content with a PIN code, pattern, or fingerprint. If you are looking for a simple way to lock your photos and videos, this app will be the best choice for you.

Simply import the files you want to hide into this app and nobody will be able to see them, even if they browse your phone. You can choose to hide the files with a PIN code, pattern, or fingerprint and you will be able to unlock them with the same method.