It's a generic problem, for example if you search for "Isaac Asimov Alapitvány" in google: http://books.google.com/books/feeds/...lapitv%C3%A1ny
google returns 11 result, but the 5th would be the exact match, the first 4 is other Foundation novels. But it's a fairly common problem, I've run into a couple of times.
Currently I try to improve the moly.hu plugin, which is a reader-community site, and provides a lot's of informations, covers, mostly for Hungarian books. Their search is similarly wide, for example: http://moly.hu/kereses?utf8=%E2%9C%9...lapitv%C3%A1ny
And if you look into one of the book-info page, for example: http://moly.hu/konyvek/isaac-asimov-alapitvany
you can see, that it shows 5 different covers - because this book is reprinted several times during the last 40 years. In this case, if you know the ISBN number, you can pick one 'correct' cover, but I think, the user should be able to pick one cover if the plug in is able to retrieve multiple