I’ve been managing SEO tests related to the alt text of images for well over 15 years, I’ve lost count the number of tests I’ve monitored: most are private SEO tests so they won’t get damaged.
I’ve had a particular public SEO test to see how Google treats the alternate text (alt text) running for about 6 years and the results have always remained consistent.
Public SEO Tests
How Does Google Treat the Alt Text of Linked Images?
The results of my SEO tests over many years is the alt text of linked images is indexed and ranked by Google the same way anchor text is treated. Alt text of a linked image passes both SEO value to the webpage the image is on AND the webpage the image link links to: in this way alt text is the same as anchor text**.
** Although alt text and anchor text are both indexed/ranked in the same way it doesn’t mean they are given equal SEO ranking value. The difference is difficult to test, but you can use commonsense: Google likes it’s users to NOT be misled/tricked.
Assuming no blackhat SEO tricks you can’t hide the text added as a links anchor text, you can semi-hide text added as alt text (it’s not visible like anchor text is and is open to keyword stuffing). If there’s a difference, Google is more likely to trust anchor text over alt text, so it’s reasonable to assume anchor text is given more SEO ranking value.
In practice use both appropriately and in a non-misleading way and you shouldn’t have any problems. If linking to a very important webpage via an image link try to add the same link, but with anchor text higher in the code so the text link is given higher priority over the image link.
How to Setup a Linked Image ALT Text SEO Test
Below I’ll teach you how to setup your own alt text SEO test while setting up a new public test which should show results within a week of publication (1st week in February 2018).
Anyone with a website can setup this SEO test.
This is the original image which I uploaded using the WordPress built in image upload feature: nothing special about the image code, standard WordPress image code.
Alt Text SEO Test of Linked Images
This isn’t the test code (that’s later), this image links to the the WordPress image attachment page and has alt text “Alt Text SEO Test of Linked Images” which by pure luck turned out to be unique text at the time of publication :-) I can’t use this text though for the SEO test, it’s been used several times on this webpage and on the WordPress image attachment page, so when everything is indexed by Google it will no longer be unique to the alt text of the image above.
It’s really hard to check what an SEO impact is if your test text isn’t unique to the SEO factor you are testing. When setting up SEO tests try to minimise variables and go for as unique as possible to make the test easier to track results. In my actual test I’ve removed the caption code and other code to keep things simple.
Linked Image ALT Text SEO Test
This is the important part of the code I’m going to use.
<a href="https://seo-gold.com/linked-image-alt-text-seo-test/internal-image-link-alt-text-seo-test-result/"><img src="https://seo-gold.com/images/alt-text-seo-test-of-linked-images-600×300.jpg" alt="A Unique Phrase Here" /></a>
It’s a basic image link which links to a deep content webpage (on this site) which is only linked to once on this webpage (this is important, see the next alt text SEO test with the homepage URL ending in #branding). It’s a slightly larger version of the earlier image linked above and I’ve removed the caption code, added class=”aligncenter” (so it looks nice, just center aligns the image), changed the URL linked to and changed the alt text to a unique phrase: a phrase currently not found via a Google search when surrounded by speech marks and I’ve not used the SEO test text anywhere else on the webpage (this is really important).
This is the test image link.
To avoid ruining this SEO test I can’t use the unique alt text phrase anywhere else on this webpage otherwise Google would index this webpage because it’s in the body text. Search Google for “SEO Consultant VALID SEARCH TEST 2” (with the speech marks) and this page will rank high and hopefully be the only webpage found because I’ve used that phrase three times in the body text (twice above and once below).
Search Google for “SEO Consultant VALID SEARCH TEST 2” including the speech marks replacing the word SEARCH with SEO.
Linked Image ALT Text SEO Test Results
The SEO test results are clear, as expected this webpage AND the linked to internal webpage is ranked for the Google search phrase above, screenshot below.
Internal Image Link ALT Text SEO Test Result
You will note only two pages are found for this Google search (not including Google ads) and the linked to result includes a “Missing: Valid 2” notice because those words are NOT present within that webpages content. The image link from this webpage is passing alt text SEO benefit through the link for those words just like we see with anchor text.
Non-Unique Linked Image ALT Text SEO Test
Let’s have another alt text SEO test using similar code, but a non-unique link with a valid anchor.
<a href="https://seo-gold.com/#branding"><img src="https://seo-gold.com/images/alt-text-seo-test-of-linked-images-600×300.jpg" alt="A Unique Phrase Here" /></a>
Same basic test setup as above, but this time the URL linked to is NOT a completely unique link from this webpage. This links to this sites home page** and there’s three more homepage links from this page (it’s not a unique link).
** The link is to https://seo-gold.com/#branding because Google has at times ignored the anchor text and alt text of links where there’s multiple versions of the same link: only counts the first links anchor/alt text as found in the code. The home page of this site is linked multiple times from every webpage of the site, there’s one link over the SEO Gold Logo (top left of screen), another link within the navigation menu and another link within the footer.
So our home page test link is one of four links to the home page from this webpage and it’s not the first link in the code, it’s the third link, but adding a link anchor like #branding to the URL means Google should treat the link as unique: it has in the past.
This is the test image link.
If you View Source (in FireFox/Chrome “Right Click” somewhere on this webpage, but not an image and select “View Page Source”) you would find the image link above has alt text similar to:
"SEO Expert VALID SEARCH TEST 1"
Replace SEARCH with SEO for the actual unique phrase.
To avoid ruining this SEO test I can’t use the unique alt text phrase anywhere else on this webpage otherwise Google would index this webpage because it’s in the body text. Search Google for “SEO Expert VALID SEARCH TEST 1” (with the speech marks) and this page will rank high and hopefully be the only webpage found because I’ve used that phrase three times in the body text (twice above and once below).
Search Google for “SEO Expert VALID SEARCH TEST 1” including the speech marks replacing the word SEARCH with SEO.
You should find this webpage AND the home page are listed for the exact match Google search if Google treats https://seo-gold.com/#branding as a unique URL.
Non-Unique Linked Image ALT Text SEO Test
Update START: Everything between Update START and END is no longer valid, Google has changed how it treats non-unique links with an anchor.
The SEO test results are clear, as expected this webpage AND the linked to home page is ranked for the Google search phrase above, screenshot below.
Non-Unique Image Link ALT Text SEO Test Result
You will note only two pages are found for this Google search (not including Google ads) and the linked to result includes a “Missing: Valid 1” notice because those words are NOT present within that home pages content. The image link from this webpage is passing alt text SEO benefit through the non-unique link with a valid anchor** for those words just like we see with anchor text.
** The URL includes #branding (an anchor), on the home page there’s a div with ID “branding”, so https://seo-gold.com/#branding is a valid anchor link.
Why Would this webpage rank for the SEO test phrases
The unique searched for phrases ONLY found as alt text within one image on this webpage, so any ranking of this webpage MUST be due to Google using alt text within linked images as an SEO ranking factor.
Why would the linked to webpages rank for the SEO test phrases?
The unique searched for phrases are NOT found at all on the linked to pages, so any ranking of the linked to pages MUST be due to Google using alt text within linked images as a ranking factor in the same way it passes ranking value via the anchor text of links.
As you can see it’s a very easy test to setup and monitor, but you have to be careful to remove any other SEO ranking factors like the unique URL issue (I added #branding to the URL of the second test).
Update END: Everything between Update START and END is no longer valid, Google has changed how it treats non-unique links with an anchor.
The above results changed in mid 2018, last time I checked this SEO test (and other copies of it) was October 2018 when the test was no longer valid.
On first examination it appears Google currently does NOT pass ranking benefit to a non-unique URL with an anchor like the test URL above: https://seo-gold.com/#branding.
What this suggests is if you have several links to the same URL like four identical links to a home page:
Text Link to: https://seo-gold.com/ with anchor text: Anchor Text One
Text Link to: https://seo-gold.com/#uniqueone with anchor text: Anchor Text Two
Image Link to: https://seo-gold.com/ with alt text: Alt Text One
Image Link to: https://seo-gold.com/#uniquetwo with alt text: Alt Text Two
Google will index all the anchor text and alt text as part of the webpage the link is ON, but only passes SEO ranking benefit to the first link as found in the HTML code. For the four links above only the first one passes anchor text ranking benefit to the home page: home page will get a small boost for the “Anchor Text One” SERP. The home page in the example above won’t benefit from the other anchor text or the alt text.
You will note I said “On first examination it appears”. That’s because if you dig a little deeper there is some ranking benefit passed to the home page via the #branding link.
It used to be the alt test above showed this webpage ranked for the test alt text AND the linked to webpage (the home page) proving ranking benefit is passed via a non-unique linked image with an anchor like #branding. Currently we only see this webpage ranked suggesting Google no longer passes ranking benefit through the #branding link, but there are image results listed for the text phrase and some of the images listed are loaded on the home page, but NOT on this webpage.
That means even though Google isn’t listing the home page for the SERP it is listing it’s images and when you visit those images from Google they take you to the homepage. So Google MUST still be passing ranking benefit via the non-unique link with the #branding anchor, but it’s not enough to list the homepage.
Further testing is required.
By setting up SEO tests like these I can be certain how Google will treat a lot of the content I create. I hate to rely on guesswork and SEO misinformation posted around the internet. Since I setup these SEO tests (and I have other identical private SEO tests) I can check how Google treats various formats of links etc…
David Law
Website - SEO Gold Services
