By the way, I should have mentioned this sooner - if you’re going to rely on embedded tags, there are a few steps to make sure Plex is configured to do so. It’s more than just the ‘prefer local metadata’ checkbox. I don’t think this is what’s causing your issues, but it’s worth pointing out.
Also, just for completeness, the album cover should be named ‘cover.jpg’ and is in the same folder as the tracks. The artist image should be in the artistname folder, and named either ‘folder.jpg’ or ‘artist-poster.jpg’.
I stole this from a post by one of the ninjas:
Music /
|--Albumartistname /
| artist-poster.jpg <--- a photo of the artist
| artist-background.jpg <--- a background/wallpaper particular to the artist
|--Albumtitle /
cover.jpg <--- album cover
background.jpg <--- album background/wallpaper [if not present, inherited from the 'albumartist' level]
1. Trackartist - Tracktitle.mp3
1. Trackartist - Tracktitle.txt
2. Trackartist - Tracktitle.mp3
2. Trackartist - Tracktitle.lrc
...