Search Engine Optimisation and multiple sub-domains per html page

Question

Hi,

We are looking for some tips over a performance and search engine optimisation (SEO) technique.

For our clients, we would like to place all of their page images in a sub domain in order to have a better browser related performance.

For example by replacing:

<img src=”/images/foobar.jpg” />

By

<img src=”http://images.domain.com/foobar.jpg” />

As stated, it seems like a good idea for performance, but our concern is :

How does this strategy performs in the SEO domain?

Thanks!

PS : Just some quick links …

Many sub-domain strategies: http://www.askapache.com/htaccess/apache-speed-subdomains.html

Only thing found stating against this use : http://econsultancy.com/blog/3559-50-seo-tips-for-online-retailers

Other interesting discussion on the topic, but not related toward images in sub-domain but microsites in sub-domains:

http://www.seomoz.org/blog/understanding-root-domains-subdomains-vs-subfolders-microsites http://www.searchenginejournal.com/subdomains-or-subfolders-which-are-better-for-seo/6849/

Answer 1

The e-consultancy tip is important if you're after decent ranking for the images you're hosting in Google Images and similar search engines.

Basically, any content on a sub-domain will effectively be at a lower rank than the content on the main domain (this is also the case if you respond on both http://www.example.com and http://example.com for example, although generally you'll then be competing against yourself), because you are leaving the core site and going elsewhere.

Certainly hosting things like CSS, Images etc on a seperate domain will help percieved performance, as most browsers limit themselves to 2-4 simultaneous connections to any one domain.

Answer 2

Well, as far as I'm concerned, using CDN shouldn't effect SEO, especially when we're talking about images.

Content of the image can't be 'investigated', so it is irrelevant. The only thing crawlers really care about are title and alt tags, so be careful with them.

As long as your pages are semantic, Google and others won't even care that much about images. Using CDN is only good, so go for it.

Of course, if you want your images to be higher at search engines, this is a whole new story.

Answer 3

If you're just using the subdomain to source images, there's really nothing you should be worrying about. It's not as though you're trying to rank images for keywords, but rather the pages those images happen to be on.

Maybe a good anecdote to explain why this is orthagonal to SEO is the fact that you can, for instance, source a link to the jQuery API on your page from Google Code without expecting any loss of PageRank. In fact, Google hosts that API in order to make it faster. If you're doing something to simply optimize the loading of objects within the DOM structure, then there's little to worry about as far as search optimization goes.

You're much better off worrying about H1, H2, title, meta description, meta keywords, and having really useful content that include the keywords you're trying to optimize for. Other than that, keyword-directed links to the page both externally and internally can help. The impact of most other things is fairly debatable.

Answer 4

This blog post from Steve Souders suggests that sharding your page's requests across 2-4 domains can be a performance benefit.

Answer 5

It's true that by loading the images, Javascript, CSS on a free-cookie domain WILL help the performance (at least for the browser).

Now talking if this will affect the SEO of your main site, the content, then I doubt that'll really affect it. However if you're asking if your images will rank lower because of that, that's another story.

The images will probably rank a little lower when people use Google Image Search but that shouldn't really affect too much.

In MY experience, I use two sub-domains for loading different part of the site and I've had no problem with it. Actually the speed improvement was noticeable and it was really worth it.