Welcome to the forum Joke9823,
I don't think that you can do this but if you can post a screenshot of which area of MusicBee you are talking about, that might help.
You can use your own 'Artist picture' (which is then saved in your library folder). When you see an artist with no image. find an image you want to use, copy, right-click on the empty image in MB and 'Paste Artist Picture'.