Just like the lyrics search option, there are option to do web search or particular genius,etc sources for lyrics.
So for album art this can be possible so it can be convenient.
What your answer is if there is wrong or no album art for particular track then the user should first download it through web and then search and select the downloaded album art. This also adds extra images in gallery. Many people won't like to do this for each song.
Simple solution would be to add web search option which is fast method and doesn't need the user to download and set the album art while also adding extra non desired images in gallary to display.