The problem here is that Amazon returns different HTML to jsoup than to your browser based on a UserAgent request.
I installed UserAgent in a well-known browser and selected the item using the identifier #prodImageand got the result OK.
eg.
Document doc = Jsoup.connect("http://rads.stackoverflow.com/amzn/click/B0051HDDO2")
.timeout(20000)
.userAgent("Mozilla/5.0 (Macintosh; Intel Mac OS X 10_6_7) AppleWebKit/534.30 (KHTML, like Gecko) Chrome/12.0.742.91 Safari/534.30")
.get();
Element img = doc.select("#prodImage").first();
System.out.println(img.attr("src"));
Returns http://ecx.images-amazon.com/images/I/51u1FaI-FHL._SL500_AA300_.jpg
, doc.html() , HTML, HTML- ( HTML HTML DOM).
, !