well, writer Brian Sibley has the backstory.
Tolkien was not amused and wrote to Rayner Unwin at his publishing house, Geroge Allen and Unwin:
I think the cover is ugly; but I recognize that a main object of a paperback cover is to attract purchasers, and I suppose that you are better judges of what is attractive in USA than I am. I therefore will not enter into a debate about taste—(meaning though I did not say so: horrible colours and foul lettering)—but I must ask this about the vignette: what has it got to do with the story? Where is this place? Why a lion and emus? And what is the thing in the foreground with pink bulbs? I do not understand how anybody who had read the tale (I hope you are one) could think such a picture would please the author.Barbara Remington, in an interview many years later, explained these curiously worrying embellishments:
apparantly, no one in the artist's circle knew what the book was about, so she made it up.
but Tolkien freaks know that it had already become a best seller via sci fi publisher Ace books (without copyright), but of course, only geeks read Ace paperbacks.