Why isn't iTunes showing the album cover for a few songs?

I'm ripping my music from my CD's to itunes. There's also an album that I downloaded one song from, so it did not come from an actual hard copy CD. For this one song the album cover is not being shown. For all of my CD's the album cover does show, so I know that whatever option makes album covers show is on. What can I do, if anything, to make it show? If it helps to know, I'm using a MacBook Pro running OS X Version 10.8.2. I'm using iTunes version 10.7. I have already added the artwork. The file for the song has the artwork, it just isn't showing up. When I choose a different option for how the music displays, (near the upper right), other options will make it show. Like the option where each album is side by side stacked on each other, or where it looks like an iPhone turned sideways, when it is set like that it will show up. But the way I have it set, it is like a list, for the music I ripped from hard CD's the album cover does show, but this one doesn't. It is not showing the blank white box, it just shows nothing.

If you right click on a song there's an option that says "Get album artwork". If this doesn't work, right click and select "Get info" or something like that and import the image yourself. You could just use Google Images to find the album artwork and save it to your hard drive or copy and paste it.