Lots more information here.
In Roon you’re going to choose a preference, meaning “if Roon finds cover art in our metdata service, and there’s also cover art with your files, this is the art that is preferred”. The default is to always use the highest quality cover art, and if only one is available, we will always use that.
If you go into Settings > Library > Import Settings and choose “Prefer File”, Roon will use the highest quality local art we can find (in file tags, folder, etc), assuming we can be sure it’s the front cover. We require that it be the front cover because we’ve seen cases where people include high res liner notes or back cover art, and if we’re not sure it’s the front it causes all sorts of ugliness.
If you have things setup as described above, and you’re not getting what you expect, please let us know some examples, including the name of the album and where the art is stored. We can definitely look into this for you, James.