Share libraries w/MySQL, guide:
1 Artwork Downloader
The Artwork downloader addon makes it easy to share artwork across a mysql database. Only one client needs to run the addon.
2 Texture Cache Maintenance Utility
The texture cache utility makes it easy to recache artwork that is stored in the database. This needs to be done occasionally on all clients using the mysql database.
This can be done from one machine as long as remote access is enabled on each Kodi install.
./texturecache.py c @xbmc.host=<ipaddress>