Ok. For this one, you need to have to have read the book and have it with you. As you've probably noticed, it refers to Janie's red hair throughout the book. In the picture on the front cover, If you read the milk carton, it says that she has BROWN hair.
Note: This may be only on certain editions of the book.
The author has no control over the cover. You can't count this as a slip-up. If you could, then I know hundreds of books that can make it into the slip-up archives. Haven't you ever heard the phrase "Don't judge a book by it's cover"?