Firstly, in case you're not aware, artworks (logo, fanart, clearart, poster, character, banner, etc) should be located in the movie's/TV show's respective folder.
For instance, below are the paths to the movie
The Dark Knight and it's artworks:
Code:
...Movies
...Movies\The Dark Knight
...Movies\The Dark Knight\The Dark Knight.mp4
...Movies\The Dark Knight\logo.png
...Movies\The Dark Knight\poster.jpg
...Movies\The Dark Knight\fanart.jpg
...Movies\The Dark Knight\banner.jpg
...Movies\The Dark Knight\clearart.png
All of the movie's artworks are in its folder.
Unless you're referring to having all the artworks in one folder, whereby you have moviename-poster.jpg, moviename-logo.png, etc. If that's the case I can't help.
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When the movie/TV show is scraped into your Kodi library, Kodi will detect the poster and fanart (don't remember if it caches the logo and banner as well). Then this is where Artwork Downloader comes into play. It loads the extra artwork into your Kodi library.
I remember having this same issue as you, where I would change a particular artwork, but it doesn't change in Kodi. What causes this is caching. The old artwork is still cached in Kodi, so you won't see the change immediately. The solution is to re-cache the artwork. I was told once that the new artwork would eventually show up after a few hours.
I didn't wait for that, so I don't know if it works. What I use is Milhouse's
Texture Cache Maintenance tool. You would have to download it and Python, and use the command line to re-cache the image. It's a great tool to familiarize yourself with because it can clean your thumbnails folder when it starts to consume too much hard drive space.