Image alt text for SEO

When optimising your website for SEO (Search Engine Optimisation), it’s important not to overlook your website images. It could mean the difference between receiving image search traffic from Google and missing out.

So if it’s so important, how do you optimise your images through image alt text?

In this blog post, we’ll explain what image alt text is, why it’s important, and demonstrate how to write it so that your images can rank highly on search engines and drive traffic to your site.

What is image alt text?

Also known as alt tags and alt descriptions, image alt text is the written text that appears in place of an image on a webpage if that image fails to load. This text also helps the visually impaired to understand what the image is by describing it to them. It also helps search engines to better understand, crawl and rank your website and its various pages.

Whether or not you actively prioritise SEO for your business, optimising your website image’s alt text is worth the effort because it helps to create a better user experience for your visitors, which is something that Google prioritises.

Why is image alt text so important?

Image alt text is important for three reasons. One is accessibility, the other is user experience, and the last and perhaps the most important one is image traffic. Understanding why alt text is important will help you write effective alt descriptions for all your website images, so let’s dive in.

1. Accessibility

It all started back in 1999 when the World Wide Web Consortium (W3C), an international community made up of a range of organisations, full-time staff, and the public worked together to develop web standards. Out of that came the Web Content Accessibility Guidelines 1.0 to explain to the public how to make content accessible to users with disabilities.

One of these guidelines was to provide equivalent alternatives to auditory and visual content. This meant that any webpage with images, whether it be movies, sounds, applets, etc, should include equivalent information to that of the visuals or auditory content found on the website.

Today this is still the case, with descriptive text alternatives to auditory and visual content meant to be in place to ensure that everyone benefits from the content you share, especially those who use screen readers to read content found on a webpage.

With this in mind, it’s easy to see why an image without a description is not helpful to someone using a screen reader, for example. For that person, it creates a poor user experience, which in some cases, could lead to a poor brand perception.

Let’s say a webpage contained an image of an upward arrow that linked to a table of contents. An example of optimised image alt text would be a text equivalent that reads “go to the table of contents”, allowing the user with a screen reader to understand the purpose of the image without necessarily being able to see it.

In essence, alt text helps ensure that your visual content is accessible to all users, regardless of whether they can see it or not.

2. User experience

Alt text doesn’t just allow for the conversion of text to audio, it improves the user experience for all users, regardless of whether they are visually impaired or not. For example, let’s say a visitor visits your site with a low bandwidth internet connection and your images don’t load. If you have alt text present, they’ll be able to see the alt text describing what the image is instead of just seeing a broken link, making for a better user experience, as seen below.

Image side by side with broken image icon and descriptive alt text that reads seven full coffee cups on wooden table

Image Source

Image traffic

Another important thing that alt text does is show your website images in search engine image search results. This could be in the form of Google Images or as image packs. An image pack is a series of images that Google displays in the search results. Image packs show up as a result of Google identifying certain search queries in which users wish to see a set of images, for example, “images of cute cats”.

images of cute cats

Image Source

How to add alt text to your images

Most content management systems (CMSs) allow for image optimisation or rich text editing, whereby you can create and change an image’s alt text. In WordPress, for example, clicking on an image will automatically open the block tab in the sidebar. Under the section marked “Image Settings” you can add the alt text to the corresponding field. Once added, you can click update from the toolbar at the top of your screen.

The most important thing to remember when writing alt text is to be as descriptive and specific as possible. It’s also best to keep in mind that alt text can lose its meaning if you don’t consider the image’s context as well. 

Image alt text best practices

Image alt text needs to be specific but also reflect the topic of the webpage it’s being written for.

Here are a few important things to consider when writing effective alt text:

1. Describe the image in detail.

2. Use both the image and the context of the webpage to guide you.

3. If the image doesn’t show a recognisable person or place, derive context based on the content of the page.

4. Keep all your text less than 125 characters. (Screen reading tools usually stop reading alt text at this point).

5. Don’t start off with “picture of…” or “image of…” immediately describe the image.

6. Use keywords sparingly. Only include the web page’s target keyword if it can easily be included in your alt text. If not, consider including semantic keywords, or just the most important keywords found within a long tail keyword.

7. Don’t over-optimise your web page by including your keyword in every single image found on that page. Only include your keyword in one image. Identify the image that you think most represents the topic of your page and assign it that keyword.

8. Review your alt text for spelling errors. Mispelled words can hurt your user experience and confuse search engines crawling your site.

Note: Not all images need alt text. Images that are purely decorative or are described in text nearby should have an empty alt text attribute. 

To make things easier, check out the below decision tree to see when to add alt text and when not to.

Alt text decision tree

Image Source

How alt text affects SEO

Alt text is used in conjunction with computer vision algorithms and the contents of the page to understand what the image is. Alt text therefore helps search engines to understand, not only what the image is, but what the webpage, as a whole, is about. 

Optimised alt text can increase the chances of your images appearing in image search results.

With Google’s Search Generative Experience (SGE), well-written and contextual alt text will ensure that your content gets included in this new type of AI (artificial intelligence) powered snapshot of key information, coming to Google’s search engine results soon.

See the below example of what we can expect.

Google AI powered snapshot

Image Source

When creating content on a certain topic, think about how your audience may prefer to find answers to their questions surrounding that topic. In many cases, searchers prefer a visual snapshot of the information on your webpage. For example, a user wanting to know how to make different shades of blue may prefer a quick summary of how to do so so that they can understand at a glance, as seen below.

How to make different shades of blue by mixing colours

Image Source

Because this image has optimised alt text, it shows up in the image search results for the long tail keyword “how to make different shades of blue”. The blog post also appears in the web search results for the same long tail keyword, which means that visitors can land on the page via two different search categories, Image Search and Web Search.

Final thoughts

So where do you go from here? Before beginning, consider performing a basic website audit of your existing content to see where you can add alt text to previously untagged images and watch to see how your organic search traffic changes because you’ve added those new alt tags.

Remember, the more images you optimise on your website, the better your SEO strategy will be going forward.