I could be way out of my league here, and stepping on toes, but I just thought you should know there is a much easier way to get covers from Amazon.
Large Image:
Code:
http://images.amazon.com/images/P/0312946201.01._SCLZZZZZZZ_.jpg
Medium Image:
Code:
http://images.amazon.com/images/P/0312946201.01._SCMZZZZZZZ_.jpg
Thumbnail:
Code:
http://images.amazon.com/images/P/0312946201.01._SCTZZZZZZZ_.jpg
The first part - images.amazon.com/images/P/ is the same for all books
The second part 0312946201 is the 10 digit ISBN
The .01 is the country code for US
The ._SCMZZZZZZZ_jpg is the instruction to create a medium sized photo. - ._SCTZZZZZZZ will give you thumb sized photos, ._SCLZZZZZZZ will give you Large size photos.
Just replace the isbn using the link above and you can generate any book cover, assuming they have one for that book.
Hope that helps.