Actually, that is called "in-line linking" or hot-linking, and is usually considered bad form since it is "stealing" bandwidth from the original site. They host the picture, it is their bandwidth used when the picture is displayed, but no one sees their ads to pay for the bandwidth. Some sites don't care, but others do. I doubt amazon will care too much, especially if you put a link to them in the post.
Just a heads-up. (although, since my work has blocked photobucket.com, when I've wanted to post a picture immediately I've done some hotlinking
)