Better Image SEO with Canonical Headers
April 25, 2014 | David Henzel
Customers often ask us if having the same image on different servers could impact SEO. We now have an official answer, as Google blogged about image indexing:
Q: “Is it a problem if my images can be found on multiple domains or subdomains I own — for example, CDNs or related sites?”
Generally, the best practice is to have only one copy of any type of content. If you’re duplicating your images across multiple hostnames, our algorithms may pick one copy as the canonical copy of the image, which may not be your preferred version. This can also lead to slower crawling and indexing of your images.
To fix the issues they’ve listed above, we’ve added a “Canonical Header” option to the Control Panel (under Pull Zone SEO settings):
This option adds a HTTP header to cached objects on the CDN, telling search engines the location of the original file on your origin server. With this information, services like Google Image Search can link to the original source in search results, and avoid crawling the same content multiple times, saving you bandwidth.
After enabling Canonical Headers, use curl or your browser dev tools to inspect the headers coming back from the CDN:
curl -I http://w3.example.netdna-cdn.com/images/matt-cutts.jpg HTTP/1.1 200 OK Date: Wed, 16 Apr 2014 23:15:22 GMT Content-Type: image/png Content-Length: 5565 X-Cache: HIT Link: <http://www.example.com/images/matt-cutts.jpg>; rel="canonical"
For MaxCDN Enterprise customers, we have added a new EdgeRules category called “SEO”. The first rule to chose from is “Add Canonical Header” which gives you more more control by allowing you to choose which file types you would like to apply the Canonical header to:
And there you have it — the link header being sent back, pointing to the canonical source. Go forth and enjoy this 1-click SEO boost.