Firstly, for all, here is the said cover -
http://www.amazon.de/gp/reader/03453...=1#reader-page
Secondly, I have no idea who drew that picture, the only idea I have is to perhaps PM
Parmastahir, he has a very large collection of Tolkien calendars, so it may well be that this picture is also to be found in one of his 1992 calendars.