“Don't judge a book by its cover.” But covers sell lots of books. More so in the past than today, the publishing industry paid professional illustrators to create the images that would sell lots of books, and magazines. 

The publisher, as a rule, sent the illustrator a copy of the book to read and then from the story the illustrator created an image that helped sell the book, sometimes regardless of the words inside. It was pure creativity. Probably more creativity than the artists of old needed to paints saints and gods, goblins and cupids, onto the walls of churches.

Over the decades Norman Adams has helped lots of publishers sell lots of books, magazines, with the creative, realistic and surrealistic images that he created for their cover.