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>I think that's a huge drawback, actually. How does Amazon's image
>service work? Does it suffer from the same issue?

No it does not. http://www.amazon.com/gp/browse.html?node=3435361 explains how it works.
You send a URL and get an XML response with lost of metadat, like the adresse of several size cover jpegs.
I also use it in our order application, so people who dor order entry have got some f the metadata alreasy in te order form as soon as they have entered an ISBN
 
Peter