The next version of the AdvancedMediaPlayerInfo plugin will also support album art embedded inside the individual audio file. Until then, we have to be content with the current version which allows us to show album art stored in folders.
The plugin uses the following conventions to check for album art :
1. It searches for a file with the name "folder.jpg" where folder=name of the folder where the mp3 is located or where folder = the name of the file itself.
2. It also searches for a folder.jpg stored in a custom folder such as the folder "C:program FilesSamurizeAlbumArt". This location can be customised in the plugin's global preferences in the Config Editor.
3. If it fails to find the album art in either of these two locations, it then searches for the album art online from amazon.com - which, as you have noted is not always accurate :/
If it fails to find the correct album art for my mp3s, what I do is delete the corresponding wrong entry from my AlbumArt folder and then download the correct one from Amazon.com. I then save it with the correct filename.jpg to the AlbumArt folder or to the folder where the .mp3 is located.
Works fine for me

Feel free to message me if all this doesn't make sense