Would the same image served from two domains count as duplicate content?
JOHN MEULLER (Webmaster Analyst from Google):
So I think, first of all, the general answer is there’s no penalty for duplicate content.This is more of a technical issue from our point of view, that if you have a lot of duplicates and we have to crawl and index those duplicates to find out that they’re duplicate, we waste a lot of time kind of crawling and indexing things on your site that are unnecessary. And maybe we’ll miss things that are more important on your site because we’ve spent so much time crawling all of these duplicates. So from that point of view, it’s more of a technical thing that you should try to avoid if at all possible than anything that would get your site penalized or would cause quality or ranking problems for your site. With regards to images, splitting them across different servers I think definitely makes sense. But what I would do there is really make sure that the individual images stay on one server. So taking, maybe, a hash or something from the URL or the image name and using that as a way to determine which server this image is served from and consistently serving the image just from that server helps kind of keep things in line. One thing that’s problematic, for example, is if you have images on your site and the URL is constantly changed so it’s shifting between individual servers every time we crawl, then that makes it really hard for us to actually index those images for image search because every time we crawl your pages, we find a new host name for that image or a new URL for that image. Then we have to kind of think about, oh, this is a new image.