I have finished updating the MAME custom artwork files. You can download the archive here:
If you aren't familiar with the extraction process, here are the steps to take:
First, backup current MAME artwork files if you want to keep them. I would suggest not backing them up. This archive replaces the following folder:
mame_emulation/artwork/
Second, copy the artwork.tar.gz file to your Pi. Then in the same folder as the file, open a terminal (e.g. via ssh) and carefully enter the following commands (copy/paste if possible):
sudo systemctl stop picochess
rm -rf /opt/picochess/engines/mame_emulation/artwork
tar -xvpzf artwork.tar.gz -C /opt/picochess/engines/mame_emulation --numeric-owner
sync
Then reboot the Pi.
Randy