Album art not matching correctly between iTunes and iPhone.

So as much as this might not seem as an issue for some, I notice that my album artwork in iTunes does not always match up with the album art on my phone. If I think that some artwork for a song or album is unappealing or not matching, I will change it to my own artwork. Normally, this has never been an issue for me until recently. What happens is I do the normal album art changing procedure (go to get info, add/delete album art) and it works fine. The odd thing is that when I go to select an album on my phone, the album art is the same as what it was in the iTunes Store and not what I added, but the individual songs have the album art that I added myself.

I've managed to fix this issue on some albums by converting them mp3 format, but that only works for some and I don't know why. I would prefer the song art and album art be the same, just because I'm really nitpicky about things matching. Am I missing a step or doing something wrong? Does anyone else happen to have this issue, or any clue what the problem might be? Help would be much appreciated, thanks!