Android: In any Linux-based operating system, including Android, you can hide files and folders easily by adding a prefix to the file name. If you want an easier interface for this, File Hide Expert is on the job.
The app allows you to easily hide pictures, videos, or any type of file. It immediately removes them from any gallery app that they might otherwise appear in. The Pro version can even disguise itself as a tip calculator, so anyone who gets their hands on your phone won't realise you have something to hide.
File Hide Pro [Google Play Store]