Thanks for all the suggestions!
I‘m going with #Faircamp by @freebliss.
https://codeberg.org/simonrepp/faircamp
It does all the things that I need the tool to do. It even does a few more. Most of which I hadn’t thought about.
I‘ll figure out if I‘m holding it wrong or if it should able to extract embedded cover images from .mp3
files.
Might just as well be an issue with the specific version of ID3 tags in those files, or my installation of ffmpeg
.