I copied rather than moved them, so I have the cover art still in the original files. I want to delete them though. I have imported them in to my library. They appear without cover art.
You didn't actually answer my questions.
Are your cover art files external disk files or are they embedded in the file tags? If they are external files what does the "Image File" field say about the filename and path? What is your selected cover art location option? (Since you have your old files in the library they should still have correct cover art links.)
By the way, are you still using MC12? (This is the MC12 board.) MC13 has a new feature for moving cover art.
You could have let MC to update the library to point to the new location. It would have preserved all statistical information and static playlists (if you have any). The smartlists should work also with the newly imported files. Fortunately, you can still do that since you have the old files in the library, but you would need to do a few additional steps.