A free app for Android, by Photo Vault – Gallery.

Photo Vault – Gallery is the best way to keep your personal photos, videos, and other documents safe from prying eyes. This utility allows you to lock your private files with a simple password, making it impossible for anyone to access them without the correct password. The app also offers a built-in calculator that you can use to hide photos, videos, and other files on your device.

Once you have hidden your photos, videos, and other documents, you can still view them if you have the correct password. To do so, you will need to enter the password that you created when you installed the app.