Image links and alt text: how a linked image passes signals

An image link is a link whose clickable part is an image instead of words: in the code, an img element sits inside an a element that has an href. An alt text anchor is the image’s alt attribute doing the job that visible words do in a text link. Google’s documentation says it uses that attribute as the anchor text, which means a linked image passes the same two things a text link does, the link itself and a description of the page it points to. The description exists only if somebody wrote the alt text. That one condition explains most of what goes right and wrong with logos, badges, infographics and embeds in link building.

What Google says about image links

Google’s link best practices page deals with image links in a few lines. For images as links, it says, Google uses the alt attribute of the img element as anchor text, so be sure to add descriptive alt text to your images. Its good example is a shopping cart image whose alt text reads “add enchiladas to your cart”. Its bad example is the same image with an empty alt attribute, which the page labels as empty alt text and empty link text. The page also describes a fallback. If the a element is for some reason empty, Google can use the title attribute of the link as anchor text. None of this changes the basic test for whether the link can be followed at all, which is the a element and href requirement covered in the lesson on crawlable links.

Google’s image guidance says the same thing from the other side. Alt text, it says, is useful as anchor text if you decide to use an image as a link. That page describes the wider purpose of the attribute: Google uses alt text along with computer vision algorithms and the contents of the page to understand the subject matter of the image, and the text exists first of all for people who cannot see the picture. Search Engine Roundtable reported in August 2019 on a question put to John Mueller about linking to other sites with images such as logos. His advice was to either have a text link as well or use the alt attribute for the image to give Google the anchor text you want associated with that link. So the documentation and the staff comment agree, and the claim that alt text stands in for anchor text is as well sourced as anything in this subject.

What is known and not known about their weight

What Google has not published is any comparison of the weight of an image link against a text link. It says the alt text is used as the anchor. It does not say the anchor counts equally, and anyone who gives you a ratio is guessing. Some reasoning is still possible from what the documentation does say. The link best practices page tells writers that the words before and after a link matter and to pay attention to the sentence as a whole. A text link in the middle of a relevant paragraph has that context by nature. A logo in a grid of partner logos has none, and its only description is two or three words of alt text. A linked image inside an article, with a caption and a paragraph discussing it, sits somewhere in between.

Position works against many image links as well. Logos and badges tend to live in footers, sidebars and “our partners” strips, which are the template areas that the reasonable surfer idea treats as less likely to be clicked. There are also image links that carry no anchor at all. An image set as a CSS background has no alt attribute to read. A linked image with empty alt text gives Google a link and nothing to describe it. A lazy-loaded image that appears only after a script runs depends on rendering. In each case the link may still be crawled, and what is lost is the part that tells Google what your page is about. For a site whose links are mostly logos, that can mean a profile with many referring domains and very little descriptive anchor text behind it.

Where image links come from in link building

Four kinds turn up again and again, and they differ mainly in who writes the alt text and how the image came to be on the page.

Kind of image link	Who usually writes the alt text	How it gets placed	Main risk
Sponsor or partner logo	The publisher	The publisher adds it after a sponsorship or partnership	Empty or generic alt text, and a paid link left without a label
Award or membership badge	You, inside the code you hand out	The recipient pastes your code	Keyword anchors spread across many sites
Infographic or chart embed	You, inside the embed code	Another site copies the image and the code	Widget-style spam if the anchor is optimised
Image used with a credit	The publisher	An editor uses your photo or chart and links the credit	The image is used and no link is given

Logos are the commonest. Every sponsorship of an event, a charity or a local club tends to end with a logo on a sponsors page, and the same is true of supplier lists, client lists and membership directories, which are the stock of partner links. These are legitimate placements made by a real organisation that knows you, and they are worth having for that reason. The catch is that the person uploading the logo is seldom thinking about alt text. The attribute is often empty, or it holds the file name or the single word “logo”. Asking for the alt text to be your brand name is a small and reasonable request, and where the page allows it, a line of text with a normal link beside the logo is better still, which is what Mueller suggested. A sponsorship that was paid for is also a paid link in Google’s terms, so expect a careful publisher to mark it as sponsored or nofollow, and do not ask them to remove the label.

Infographics and charts are the kind that link builders once produced in bulk. The lesson to take from the page on linkable assets is that an infographic rarely earns links by itself any more and works as one part of a data campaign. Where a chart or map does get picked up, the link you want is an editorial one in the text of the article that uses it, written by the journalist, and not a link wrapped around the image by an embed code. The embed is a fallback for sites that would otherwise copy the image and credit nobody.

When image links become widget spam

The risk sits in the second and third rows of the table, where you write the code and other people paste it. Google’s link spam policy lists keyword-rich, hidden or low-quality links embedded in widgets that are distributed across various sites as an example of link spam. A post on Google’s webmaster blog in September 2016, titled as a reminder about widget links, set out the reasoning. Some widgets, it said, add links to a site that the site owner did not editorially place and that contain anchor text the owner does not control, and because such links are not naturally placed they are treated as a violation. The post said Google’s webspam team may take manual action on them, and that the fix is to add a nofollow attribute to the widget links or to remove them.

An image badge fits that description exactly when its alt text is a commercial keyword. Suppose a comparison site for language courses hands every school it lists a “recommended school” badge, and the code behind the badge links to the comparison site with the alt text “best online Spanish course”. Hundreds of schools paste it. The result is hundreds of links with an identical keyword anchor that none of those schools chose, and that is the pattern the policy describes. The same badge with the site’s name as alt text and a nofollow attribute is unremarkable. The lesson on sitewide, footer and widget links sets out the compliant form of credits, badges and embeds, and Google’s link spam policy puts the widget rule beside the other examples.

Hidden image links belong to the same family and are worse. A one-pixel image, or an image styled so that nobody can see it, wrapped in a link with keyword alt text, is a hidden link under another name, and it is one of the things to look for when you check a page you have been offered. Old directory and profile networks, the kind covered in the lesson on old-school links, often mixed text links with small linked banners in the same way and are discounted for the same reasons. If you inherit a site that once ran a badge or widget campaign with keyword anchors, the practical step is to change the code you distribute, ask the larger sites to update theirs, and treat the rest as links that Google is most likely ignoring.

Writing alt text for a link you control

Alt text has two readers, and the first is a person using a screen reader. Good alt text describes what the image shows or, for a linked image, where the link goes. For a logo that links to your homepage, the brand name is the honest description and also the right anchor. For a linked chart, a short phrase naming what the chart shows does both jobs. Google’s image guidance warns against filling alt attributes with keywords, which it calls keyword stuffing, and says it results in a negative user experience and may cause a site to be seen as spam. A sentence of search terms on a logo fails both readers at once.

Alt anchors count in your anchor profile like any other anchor. When you plan anchor text across a set of placements, the logo links and badge links belong in the same tally as the text links, and they should fall almost entirely on the branded side. That is the natural result in any case. Organisations that display your logo describe it with your name, so a profile where image links carry commercial phrases looks arranged. The general rules for anchors, including why no safe ratio exists, are in the anchor text lesson. Where you supply the code yourself, keep it plain: a normal a element with an href, the image inside it, the brand or the asset title as alt text, and a nofollow attribute if the code will be handed out in bulk.

Checking and reclaiming image links

Checking an image link takes one step more than checking a text link. Open the page source, find the a element that points to your site and look at what is inside it. If it is an img element, read the alt attribute. An empty one is worth an email to the publisher, and so is an image that turns out to be a background with no link at all. Backlink tools differ in how they show image links and their alt text, so it is worth confirming a sample by hand before trusting a report on anchors. The backlink status checker on this site confirms whether a page links to you, whether the link is followed and whether the page can be indexed, which settles the questions that come before the anchor.

Images also produce links you are owed and never received. Photos, charts and logos get reused without credit, and a polite request for a linked credit is one of the easier forms of outreach because the publisher is already using your work. The method, which starts with a reverse image search on your originals, is described under link reclamation. When you ask, ask for a credit in text beside or beneath the image, with your name as the link. That gives you a visible anchor in the body of the page, which avoids every weakness of the image link in one move. Terms used here, including image link and alt text anchor, are defined in the glossary.