miromente wrote:
I've found a SOLUTION...
The workaround goes as follows
- create or download an empty 1sec mp3 file
- rename it to 'cover [album].mp3'
- put this into the album's folder
- import it to your library
- assign the right information of the matching album (title, artist) so it will show up with the other songs of this album
- assign the cover art manually to this specific mp3
Then it's ready to go and you can enjoy your WAV music with artwork.
But that only associates the artwork with the MP3 track, not every individual track.
In an Album View in iTunes, yes, you will see the artwork. But when you play a wav file track, no artwork will appear So when you play the WAV track, no artwork:
On this album shown below, I have one track set as an MP3 file while the rest are WAV files. As you can see, iTunes has picked up the artwork on the MP3 track and displayed it as the album artwork when looking at the album (larger view in 2.). If I play the MP3 track, the artwork is shown in the Now Playing (3.)

and if I click on the little thumbnail (3.), the display is:

But if I then play a WAV track, we have this:

and

And on my iPod Classic the same thing happens. The artwork is displayed is an "Album view" but not when an individual track is playing.
The question posed by the original poster was: "why isn't it possible to add artwork to a WAV file" and it was also stated that "the is question has been asked many times, but with no real answer".
Yes, it has been asked many times, but despite getting a real answer, far too many people choose to ignore it simply because it doesn't give them what they demand.