No thumbnail on artist view?

Hi.

On my music(this music that I am referring to not directly bougt from iTunes) there is no music album artwork thumbnail.

I inserted it on a song by >get info>artwork>add. Now when you go on artist, for this album only, nothing shows and is a blank thumbnail. But when you click on it so you are looking at a page full of that albums songs, the artwork is there. Any help?