Just to add ....
If you download media files without the Roms. I use an application called "FatMatch" , its from EmuMovies . just google it ( Not sure If I am allowed to post a direct link)
Super simple to use. Select your Roms Folder and select your relevant media folder, for the roms you wish to add media to and it will produce the correct names for the Images/Videos to use on LB.
Just press start.
Then move the media files to the correct folders.
Simple as that, If I can use it , anyone can !!