The watercolours, painted by artist Cliff Wright, are featured on the second and third instalments of the book series, reported Contactmusic.
One of pieces, which was featured on the cover of 'Harry Potter and the Chamber of Secrets', depicts the boy wizard and Ron Weasley in a flying car and is being sold with a reserve price of 12,500 pounds, while the second is taken from 'Harry Potter and the Prisoner of Azkaban' and has a minimum bid of 7,813 pounds.