The covers of picturebooks signal the theme, tone, and nature of the narrative, as well as implying an addressee. Few artists create a unique cover picture not repeated inside the book. The choice of cover evidently reflects the importance attached to the particular episode.
– from How Picturebooks Work by Maria Nikolajeva and Carole Scott
…illustrations in children’s books contribute to our perception of character, giving an instant and immediate external portrait. Even when a novel is not illustrated, a cover picture may be revealing enough. Even a very brief examination of a number of covers to classics such as Anne of Green Gables shows how a visual portrait of a character can influence our expectations. In existing covers, Anne is portrayed sometimes older, sometimes younger, sometimes happy, sometimes sad, sometimes very pretty, which contradicts the text, and sometimes plain, in consistency with the text. In any case, the cover signals that the protagonist is a young white female. This may make adult, male, and non-Caucasian readers reject the novel.
The covers of Roll of Thunder and The Planet of Junior Brown show black characters, filling the gap left by the text and signaling the characters’ social status. Book covers are paratexts that contribute to our understanding of the character. Unlike adult novels, it is almost inconceivable that a children’s novel would not have a cover illustration. A character’s portrait on the cover or in illustrations enhances the verbal description of the character or replaces it.
– from The Rhetoric of Character In Children’s Literature by Maria Nikolajeva
A Book Cover In Time: The Changing Art Of Our Childhood Reads from The Atlantic
Book Cover Monday: Strong Females, from Rabia Gale