[mikezerosix]

It is a mess atm. 

I think the root of the problem is TMBD deleting almost the their images or just generating new URLs for them. Currently Kodi just can not cope with this. Specially if you are using (mysql) DB.

Once the library listing is added the URL for artwork is permanently store and Kodi assumes that the URL will remain functional forever. As they have been for years. But now that TMDB started messing with the image URLs that is no longer the case. 

So we need :
1. Persistent storage for the artwork, specially when using the DB. Just use the DB BLOB field. Maybe setting to choose is user want to persist the artwork data. The cache thingie is not working, specially when multiple kodis in the house using same DB.    
1. "re-fetch artwork" function to context menu and/or to information view. We do not want to re-fetch all the item information and lose our own information like watched status. Just the Art work. 
2. Clean library should validate the artwork URL are valid (NB: request for image to TMDB return HTTP 200 status and HTML error page to mess up diagnosis) so it needs to actually validate the response is binary image file. 
3. maybe (settings) to automatically discard artwork that retrievable on showing it. And to search a new one.

[Karellen]

I think the root of the problem is TMBD deleting almost the their images or just generating new URLs for them

Yes that has caused most of the problems with artwork, especially for older established libraries.
Which is why I cannot stress enough... Use local artwork. Scrape your media, Artwork Dump downloads the original artwork, and you never have a problem again. Excluding drive failures.

1. Persistent storage for the artwork, specially when using the DB. Just use the DB BLOB field. Maybe setting to choose is user want to persist the artwork data. The cache thingie is not working, specially when multiple kodis in the house using same DB.    

Actually most of the team want to go the opposite way. They want all artworks links removed from databases.

1. "re-fetch artwork" function to context menu and/or to information view. We do not want to re-fetch all the item information and lose our own information like watched status. Just the Art work. 

Requires an artwork only scraper. Any volunteers??

Clean library should validate the artwork URL are valid (NB: request for image to TMDB return HTTP 200 status and HTML error page to mess up diagnosis) so it needs to actually validate the response is binary image file. 

Never.
Think about it. There are millions of users of Kodi. A high portion of those use libraries. If Kodi had to check every siingle link in your db, on larger libraries, it could lock up Kodi for hours or days.
Then think about TMDB. Do you think they would be happy to receive billions or tens of billions of extra api calls?

3. maybe (settings) to automatically discard artwork that retrievable on showing it. And to search a new one.

I don't really understand this one.