Cannot get updated album artwork to display properly

Has this happened to anyone else lately? I tried to update the album artwork for some of my music in iTunes via copy-and-paste in the song info but something's not working right about it. When I paste the artwork into the appropriate place the image doesn't display, even though the blue highlighted square shows that something is there. The album art display in iTunes itself is completely blacked out when the song in question is selected or playing. I've shut iTunes down and restarted it but this has not solved the problem.

Kim