Album Artwork is Incorrect on Phone

I have a Weird and Annoying problem. I have synced my Music to my IPhone through my Mac. The album pictures are wrong. The titles are correct, but the artwork isn't. I have tried to un-sync my Music, I unchecked the box that says "Sync Music to Iphone." It takes out the playlists, but the music is still there with the incorrect artwork. How do I fix this problem? Why is the music still there when I have unsynced it? I need this fixed. I know it sounds like I'm making a big deal out of nothing, but it's my music. I want it to be correct on my phone.