Regarding the sandbox API's, I think all of the images don't work, or at least they didn't for me. I believe all of the images were placeholder images, and clicking on them takes you to an unloadable page (at least in my experience). Using the same implementation but with the production keyset and API's, the images work just fine. If you look at the browse API documentation, for item_summaries, there are a couple ways to get image URL's; I think there is a thumbnail image and an array of images returned from the API along with the rest of the information. I don't know how you would directly download the images, but at the very least you should be able to open the production API images in a tab and download it from there. I hope this helps!
