Itunes on SD - how to add artwork?

Hi

I have saved all my iTunes music to an SD card as my laptop has small memory. Many of the albums have no artwork. I have selected the song, found the Artwork and added it but it does not appear in Itunes when I look at Albums

What am I doing wrong?

Thanks

Most probably you forgot to reimport/refresh your iTunes library for your updated songs.
(I assume you have added the artwork with Mp3tag, right?)

Many existing threads here says that iTunes has his own database to manage cover art.

This is correct. The iTunes database needs to be refreshed. You can run an internet search to find a script that will simplify this for you, there are a few out there.