Hello Nikicampos
I have no such problem with iTunes with a library of more than 30000 songs.
I used to be a Weekend DJ with many many Albums.
Which view in iTunes does not give you an Artwork.
One thing to note is the list view, will give you an Artwork only if there is more song than the size of the Artwork icon.
here is an example
I left only two song in the Hush Album to show that list view, wont give you the Artwork in this case.
but as you can see, the info of the selected song show the artwork.
in the finder, without Icon Preview checked, you wont see the artwork.
With icon Preview Activated
I do have more question
Why do you convert the song ?
if the original song is an aiff, wav or a movie, the artwork cannot be inserted inside the file, so converting it will result into a song without artwork.
Sometime you will see a file marked MPEG-3 but it is a video. Open it into Quicktime, export it as a audio file then put it in iTunes, and if the file is mp3 or mp4, AAC, then you can insert the Artwork.
I probably dont fully understand your problem, give me more info but I am using iTunes since the very first version and I never hard a problem with artwork.
Could you give more detail about your problems?
Thank you
Franco