Sometimes Album art may not be avaliable or you would like to add your own here is how you do it.
- Open iTunes and go to your Music Library. View it in Grid View so that all of your albums are displayed.
- Right–click the album whose album art you wish to change. Select Get Info.
- When asked if you are sure you want to edit information for multiple items, click the Yes button.
- Go to the Artwork section and double-click on it.
- Browse to the desired album art and click the Open button.
- The songs will be updated with the new album art and it will then be displayed in your Music Library.
You can also Copy & Paste Album art directly into it by right clicking the image you want and select copy. Then right click the Artwork screen in iTunes and select paste.