"App Lock" and "Vaulty" Hides Pictures lets you password protect Android apps, files, videos ect.

App Lock

Android lets you protect your device by creating a password, PIN or gesture lock to keep people from using your phone without your permission. But what if you don’t want to secure your entiredevice? There’s a free program called App Lock which lets you password protect individual apps, files or photos on your Android device.

When you first run App Lock, you need to login with the default password. It’s 1234. I suggest you change it as soon as possible.

Once you’ve done that, you can click the Lock, File Lock, or Shield Pictures buttons on the home screen to start protecting your data.

From the main Lock menu you can view a list of apps an choose those you want to protect. For instance, if you don’t want anyone reading your email or sending text messages from your phone, you cam check the boxes next to Gmail and Messaging.

The File Lock menu open a file browser. You can tap-and-hold on individual files to lock or unlock them from this view. The Shield Pictures function shows you a list of directories with photos in them. You can check boxes next to any photos you want to password protect.

App Lock will only work if the program is running, so password protecting files won’t do any good if you don’t leave the application on. Andthere’s nothing preventing someone from uninstalling the app if they gain access to your phone — so it’s probably best used to keep your kids from sending prank messages from your phone rather than as a fullproof security tool.

Vaulty

The best app to hide pictures and videos.

If you want even more privacy, check out "Hide Pictures in Stocks App"
You can hide pictures and videos in a fake stocks app and no one will ever know. It works just like a stocks app unless you enter your password.

Keep your private pictures and videos private with Vaulty. Do you have pictures or movies on your phone that you don't want your friends, coworkers or kids to see? Hide them with Vaulty Free! Just open your gallery, select the pictures or videos you want to hide and then select share & pick Vaulty to hide the media. Open Vaulty and enter your password to see you hidden pictures. Press menu & select Videos to view videos. Press menu, select options & then tutorial for more info.

Hide pictures and videos. Use Vaulty to hide pictures and videos.