WordPress Version: 3.3.1
Wordpress SEO Version: 1.1.7
Plugin Author: Joost de Valk

Problem: Canonical links turned on for non-duplicate content pages.

Having been happily using Yoast’s WordPress SEO on a customers WP e-Commerce health products site for some time I decided to implement it on my Japanese Arts gallery hobby site.

The Japanese Arts gallery site uses the NextGEN plugin to manage the gallery albums and images. Having deactivated the All in One SEO plugin and Google XML Sitemaps I installed and activated WordPress SEO by Yoast and everything looked pretty good. The settings import function is excellent – loads of time saved there.

On closer checking however, it appears using WordPress SEO has reintroduced a canonical URL problem I previously had on the site.

The problem is that after clicking on a gallery thumbnail the NextGEN generated image page that’s opened has a canonical URL set pointing back to the gallery thumbnail page. However, both the gallery thumbnail page and image page have unique content. The vast majority of my content is on image pages which include text/descriptions so to have them listed by site review tools and potentially treated by Google as not to be indexed is a serious issue. I resolved this previously by commenting out the add_action for rel=canonical from the default-filters.php file in WordPress.

Obviously this is not a ‘fault’ with WordPress SEO given this problem existed previously – the problem is that the plugin does not let the user choose if they want to use canonical URL’s or not. The resolution is simple – remove WordPress SEO and go back to using All In One SEO which very usefully has a setting to turn canonical URL’s on or off. Unfortunately Yoast’s WordPress SEO doesn’t have such a feature (please correct me if I’m wrong). I’m not sure why that functionality isn’t available given the number of forum issues that are reported for canonical URL problems.

An additional thing I noted in the short time I used WordPress SEO on the gallery site was that the xml sitemap function didn’t include any of my sites translated pages. I use a translation plugin to bulk up my site and because many of my visitors are from non-english speaking countries. My previous sitemaps generated by Google XML Sitemaps do include the translated pages and Google has most of them indexed.

If your a NextGEN gallery user be sure to check that ‘sub/child/nested’ pages of your site are not set to be non-indexable (even though Google doesn’t always adhere to that). You may be better served using All in One SEO with Google XML Sitemaps and Robots Meta.

Yoast WordPress SEO Canonical URLs Turned On Example Image

Yoast WordPress SEO Canonical URLs Turned On

Update: 2012/05/25 – Response from Joost de Valk (aka Yoast).
Hows this for great service. We posted a short version of the post above on the WordPress forum and Yoast responded the same day.

I’m not going to add a setting for it, as that is bound to confuse people, but adding this to your functions.php does it nice and simple:
add_filter( 'wpseo_canonical', '__return_false' );

If your having a problems with canonical URL’s while using WordPress SEO then using the above filter will turn them off.