The album art converter is the the album art INSIDE the game. What you’re trying to do is change the image on the file when you look at it on your console’s HDD, which is something else entirely. If your intent is to actually change the album art inside the game, you’re doing it wrong.
You are about to leave Rhythm Gaming World and access the external songs DB. While no song or file sold for commercially available videogames is hosted there and only fan generated content is allowed, Rhythm Gaming World has no direct control over the database and no files are hosted here. Alright, we had to made you aware of this, now you can visit the database!