In short, alt text is an attribute that is added to the html of a page to tell the user what is contained in an image. There are various applications of alternative text in SEO and web development circles, but the most important point to note is that it should be an accurate description of the image itself  nothing more, nothing less. (Note: whilst these are technically ‘alt attributes’, they are commonly referred to as ‘alt tags’. Potayto, Potahto…)

Does the user see an image’s alt text?

If you were to land on a web page that is displaying and functioning properly, you would not immediately be able to see the alternative text on an image. Instead, you would just see the image. However, there are certain instances in which the alt text would be displayed to the user:

  • When the browser cannot render the image (usually due to slow internet connection)
  • When the user has a screen reader – an accessibility function commonly used by users who are visually impaired or partially sighted
  • When the user has set their browser to text-only mode or has disabled images on their browser (again, usually due to slow internet connection)
  • When the user hovers their cursor over the image

Why is alt text important for SEO?

A picture says a thousand words… to humans. Unfortunately (or fortunately, depending on on your view of AI) Google is not a human being and is therefore limited in its capabilities. Although Google cannot ‘read’ the content of images, some have claimed that Google can read text within an image. But we tend to prefer taking information from the horse’s mouth, and in their Webmaster Guidelines Google explicitly say that their crawler cannot read text in images. This may change as OCR (Optical Character Recognition) advances, but at the moment they advise simply using alt text to provide a description of an image. This isn’t just for the user’s sake, but also for Google’s!

As web design rapidly moves towards less text-heavy sites and more image-led ones, Google is forced to work with much less information that the crawler can read (i.e. text). As a result, alt attributes can be used to fill in the gaps of Google’s knowledge, i.e give a description of an image’s content. Google also recommend that you include some descriptive text in the content around the image as well as in the alt attribute.

As is the theme with all of our SEO tips, the alt text of an image should be an accurate description of the image itself. In turn, for the sake of user experience, your images should be relevant to the text on the page and the subject in question. All this emphasis on relevance and accuracy makes alt text a good place to add some useful search terms.

Since it acts as a description of images, alternative text is a key factor in image search. Whilst SEO is mainly focussed on organic search results, you can’t ignore the importance of image search when dealing specifically with images. Including great imagery on your site which then ranks on image search should be viewed as another opportunity to capture your target audience. The title of the image should also be optimised, replacing those jumbled numbers that are automatically outputted by cameras or phones (just make sure that your title and alt text are relatively similar).

Technical implementation of alt text

In most CMS’ there will be an alternative text function to each image. In WordPress, simply click on the image once it has been uploaded to the gallery and there will be a box on the right hand side underneath the image title with a caption that says ‘Alt Text’.

The code for alt text is as follows:

<image src=”” alt=”insert alt text here”/>