The image, taken by Paris-based fashion photographers Sofia Sanchez and Mauro Mongiello, shows a doll-like girl wearing a pink fur coat and make-up.
Author Joanne Harris tweeted: "Seriously, Penguin Books. Why not just get Rolf Harris to design the next one?"
Writer Lucy Coats, the author of more than 30 books for children, told The Bookseller: "It is sexualised and has nothing to do with the book."
The picture is used on the Penguin Modern Classic version of the book which is intended for adults and one of three editions of the novel being published to mark 50 years since it first came out.
Penguin are publishing another two Dahl books, including the short story collection Someone Like You, as modern classics.
The publisher said: "Ready for Charlie And The Chocolate Factory's debut amongst the adult titles of the Penguin Modern Classics list, a new cover image focuses on the children at the centre of the story, and highlights how Dahl's writing embraces both the light and the dark aspects of life.
"This new edition of Charlie And The Chocolate Factory celebrates 50 years of the bestselling and beloved classic. The story of Charlie Bucket, a mysterious, eccentric chocolate factory owner and the golden ticket that transforms his existence is a masterpiece of exuberant invention, nonsense, fantasy and dark morality tale; both delightful and cruel."
Dahl's novel, which has inspired several film versions and a hit stage musical, follows the adventures of young Charlie Bucket inside the chocolate factory owned by the eccentric Willy Wonka.
It has sold more than 20 million copies worldwide and is currently available in 55 languages.