Itunes album artwork

[GSA190]

I just noticed that I have all of my album artwork on itunes but when I look at my iPhone some of the art work has the "?" symbol where the artwork should be. What is wrong with that?

Another question. All of my music is under the right album artwork in itunes but on my iPhone some of my music is under a different artwork picture. For example, Aesop rock's song "Easy" has different album artwork then it should be. It's art work is Tom Petty's album artwork. What is the problem? Thanks in advance.