Two original “Harry Potter” book illustrations, Winston Churchill’s resignation letter, a dress worn by Princess Diana and documents signed by Adolf Hitler are just some of the eclectic items put on the block by auction house Nate D. Sanders. The “Harry Potter” illustrations by British artist Cliff Wright were used as the covers for the second and third installments of J.K. Rowling’s seven-book series that has become one of the best-selling books worldwide.