File:ThePenultimatePeril.JPG

Summary
Cover of TPP

Fair Use in The Penultimate Peril
I believe that this picture of a book cover comes under fair use as it does not hinder the publisher or the author's ability to sell the book, it is used for an encyclopaedic purpose to show what the cover of the series looks like, and it is not shown at full size on the articles it is found on. There is no free equivalent of this book cover, so the image cannot be replaced by a free image.

Source
Derived from a digital capture (photo/scan) of the book cover (creator of this digital version is irrelevant as the copyright in all equivalent images is still held by the same party). Copyright held by the publisher or the artist. Claimed as fair use regardless.