Why can't I add artwork to my music in iTunes?
One reason the Add Artwork button can be grayed out when selecting a song in iTunes and then Get Info, is the file does not have write permissions set.

Select the song in iTunes and then right-click it, then select Show in Finder.

In Finder select the file and then right-click it, then select Get Info.

Under the Sharing &amp; Permissions: does it show Read only for you?  If yes change the permissions so you have Read &amp; Write permissions.

The image below shows Add Artwork grayed out when the file permissions are set to Read only.



The image below shows Add Artwork active when the file permissions are set to Read &amp; Write.



If it shows Read only for you, then click the Lock icon on the Get Info sheet and enter your password and then click the arrow next to the permission for Your Name (Me) and select Read &amp; Write, then click the Lock icon.



Another reason can be the file type is not one that supports manually embedding artwork, such as a .wav file. That said, artwork should be able to be added through the iTunes Store which will save it separately if it's not a file type that supports embedded art work.