Managing Thumbnails in folders?

[Anoles]

I am making a lot of folders on my tablet for movies, tv shows, music (albums, artists, mixes, playlists) - and I want big, high-res thumbnails for everything. My question is, how and how specific can I get? Do you just throw thumbnail.jpg into a folder with MP3s and that is that folder's thumbnail? Is it from meta data? And what about thumbnails for individual video files all in one folder?