Prevent Using Posters from Files

[Alcoholic]

Any particular reason you have local images but DON'T want Jellyfin to use them?  AFAIK, Jellyfin will ALWAYS prefer local images and I'm not aware of a setting to change that behavior.

Some movies come with screenshots which have the exact same name as the movie file which Jellyfin prefers, as shown in the screenshot.

I understand that.  If you don't want Jellyfin to use them either rename them or remove them.  Jellyfin will ALWAYS use local images when named the same as the movie or as one of the other file names supported (poster, folder, backdrop, cover, etc).

I've only just realised that the "Edit Images" option has the ability to download images from the internet that replace the preferred one without actually affecting the file, so this seems to be a good option for me now. Thanks for the recommendations.