UPDATED: Save Album Art to Album Folder v6.9
For macOS 10.15 and later only. This script will export the artwork of the selected tracks (or the tracks in a selected playlist) as an image file to the folder which contains each selected track's file--presumably each track's Album folder--or a single user-selected folder. If multiple album tracks are selected, the script will make sure only one artwork file per Album is exported.
More information for Save Album Art to Album Folder v6.9 and download link is here.
Also see Save Album Art as folder.jpg.