I have a USB reader in my car, and the display shows the song title and artist of what is being played. I knew that information is readily available in the MP3 metadata. But I am also seeing the album cover. Is that information actually stored in the MP3 metadata also? I thought part of the design philosophy of MP3s was to keep the file size down but it seems like adding graphics would subvert that goal.
It is stored in the ID3 tags along with the rest of the metadata, in each MP3 file. Wikipedia has a brief overview of the ID3 format.
The album covers themselves are generally not super high-res, but they do certainly take up space. Worse is the fact that MP3 has no way to reference any kind of external resource, so you’re storing a copy of the album cover in every single song from that album.
But if you’re really pressed for space, you can use whatever MP3 manager you like to delete the cover art images.
From id3v2 spec:
Apparently some of the “picture type” codes can be quite specific.