I recently read about a conflict between an author and her publisher regarding book cover images. It wasn't just a situation of artistic differences--the publisher chose a cover showing the face of a white girl when the main character of the book is black.
The author, Justine Larbalestier, explains the situation very well here. The basics: the publisher felt that books with black people on the cover don't sell well, and they wanted a photo of a girl on the cover, so they went with a white girl. Since the book is about an obsessive liar trying to mend her ways, the publisher didn't feel that having a mismatch between the cover and the character's description of herself was a big deal.
I work in publishing, so I understand that cover images are very important to a book's commercial success. And as writers we should all be concerned about our commercial success because, after all, we want our work to reach people and we want to get book contracts in the future. But c'mon. There are clearly ways to satisfy the needs of the marketers and the integrity of the book. (The sad fact that racism affects book buying is a whole 'nother matter.)
That said, one positive thing about this controversy is that people are talking about the book. I, for one, am going to read Liar, which I may not have heard of if it weren't for the ill-chosen cover.