A free program for Android, by Perceptive Apps.

Hide photos, videos, audio, documents, and more using Photo Video Locker. This tool is a very simple and easy-to-use application that helps you to maintain your privacy on your Android device. With this application, you can easily hide private photos and videos from the gallery and prevent others from accessing them. 

If you want to use this app, you will need to first create an account and enter a PIN. Once you have done that, you will be able to access your private files. You can also lock the app with a PIN or password to prevent others from seeing your private files and photos.