iTunes album cover is not the correct cover for that album
Solution 1:
You can look for covers yourself (i.e. on Amazon or w/ Google Image Search) and copy & paste them in the "Get Info" dialog (select all songs of an album, press Cmd-I, paste the image into the "Artwork" area).
There are tools like CoverScout which automate these tasks which is feasible if you have a large music library w/ lots of broken covers.
Solution 2:
Sometimes iTunes thinks the CD tracks you have are for a different album (happens more for lesser known CD's.)
An option you could use is to find the Album art online and then manually insert them as the Album art.
The way to do that in iTunes:
- Right Click the song you want
- Select Get Info
- Click the Album art tab
- Add and select your album art
Note: Can do this for an entire CD by selecting all the songs and then changing the Artwork section under the info tab