Hiding your files from the Media Scanner
Include an empty file named .nomedia in your external files directory (note the dotprefix in the filename). This will prevent Android's media scanner from reading your mediafiles and including them in apps like Gallery or Music.
---------------------------------------
If you don’t want the system’s media scanner to scan the media files of your application, create an empty .nomedia file in the application’s media files. This will prevent the media files in the application from being scanned by the system’s media scanner. It also includes apps like photo gallery or music player.