This question contains an example of a potentially infringing work, but I believe it is fine because the book does not contain copyrighted images and is basically a discussion of another book.
My understanding is fair use applies as described by another Stack Exchange answer here.
I've seen "unofficial books" at Barnes & Nobles that contain copyrighted images such as the one below. I believe the images infringe copyright in such cases, as the author is not the copyright holder.
Who is likely to get sued, the publisher or the author?
I feel like the publisher should know better than to publish copyrighted material. Is it their responsiblity?
Disclaimer: This is an example. I don't know if the book above actually has permissions to use the art. For the sake of this hypothetical question lets pretend the artwork was not authorized.