Download texturecache.py from https://github.com/MilhouseVH/texturecache.py

wget https://raw.githubusercontent.com/MilhouseVH/texturecache.py/master/texturecache.py
chmod 755 texturecache.py
#reload/replace even if it exists
#./texturecache.py C @webserver.username=kodi @webserver.password=kodi @allow.recacheall=yes

#load only missing artwork
./texturecache.py c @webserver.username=kodi @webserver.password=kodi

#reload only missing artwork of specific class and including a filter:
./texturecache.py c movies earring @webserver.username=kodi @webserver.password=kodi

Kodi stores artwork path references in its database table 'art'. Truncating this table and running Artwork Beef, refreshes all of your art.

Step-by-step guide:

• Install Artwork Beef https://forum.kodi.tv/showthread.php?tid=258886 (not really kodi19 compatible!)
• Close Kodi on all applicable devices
• Make sure you have a backup of your database
• Connect to your database
  • If you are using shared libraries via MySQL, use a MySQL client to connect to the database. Make sure to “use MyVideos<DBNUM>;” on the correct database. If you are unsure which version this is, check your kodi.log file.
  • If you are using local databases, download an SQLite client (like DB Browser for SQLite)
• Select your database and run the SQL query truncate table 'art';
• Delete the Thumbnails folder under the userdata folder
• Delete the Textures<DBNUM>.db file from the userdata/Databases folder
• Start Kodi
• Run Artwork Beef