[HomerJau]

That’s a limitation on the current Music Video implementation in Kodi. The Artist image comes from the Kodi Music Library Artist image. The Music Video Library doesn't have artist images. A nice feature would be for MVs to use an ‘artist.jpg’ image in the ‘album’ folder or similar feature.

So the missing artist images are artists you don’t have in your music library, Kodi defaults to the headphone image (or the skin maybe).