What is an image alt tag?

An image alt tag is text that provides a text alternative for visually impaired visitors who can use a screen reader to hear what the image is, and also for search engines to better understand what the image is. Your website editor may call it Alt text, Alternative text, or Description.

The code looks like this: <img src="/url" alt="context of image">

I mention this not to show off coding knowledge, but to help you visualise how it's used on a web page. Think of the alt text as something that explains the image on the page. Don’t include alt text that isn’t related to the image and the page.

Note: Unlike meta titles and descriptions, there is no official recommendation on how long image tags should be so focus on using as many words as needed to best describe the image and its context.

When writing image alt tags, keep these 3 things in mind:

  1. User purpose: The words should help someone who can’t see understand the intent & context of the image on that page - so you're not looking to describe the image in detail, but rather why you've included the image on the page
  2. Primary SEO purpose: image search results
  3. Secondary SEO purpose: image alt text appears on the page so it can help the page’s ranking
“... use it as something that applies to the image, and I would use it for usability reasons and for Google Images to better understand that specific image” John Mueller, Google's Search Advocate

3 Steps to writing optimised image alt tags

Step 1: Focus on context

Write a description that describes why the image is on that page & what the intent is. The goal isn't to say what the content of the image, but to describe why that image is being used on the page.

“When it comes to Google Images you don’t need to describe exactly what is in the image, but rather kind of what this image means for your particular page”John Mueller, Google's Search Advocate

Step 2: Be descriptive

Use as many words as needed to help someone imagine the image’s context. There’s no upper limit, but like in page content, don’t keyword stuff.

Step 3: Be specific

The image alt text should be specific for that image on that page & be different from what’s written on the page, including other image alt tags. So it's not a copy & paste job, but an opportunity to expand on why that image has been used.

Putting all that together, let’s say I’m writing image alt tags for a page on a Putney community website talking about a local event:

Bland alt text: “A bird on the grass”

Better alt text: “A robin on Lower Putney Common spotted during the April nature trail event”

See what I did there? Be specific and describe the image in relation to what the page and site are about.

You can listen to John Mueller's SEO office-hours about image alt tags: video is queued to start at the point the quotes I've used start from

Additional considerations

  1. The filename matters - use one that provides basic context. E.g. WA002-3326.jpg means nothing so rename it to “Glass-of-water-on-desk.jpg”
  2. Find the balance between image quality & speed - bigger images take longer to load but if the image is too small for its space it’ll blur when resizing up.
  3. If your image is a link then the alt text is what will be used as the anchor text

Google uses alt text along with computer vision algorithms and the contents of the page to understand the subject matter of the image. Also, alt text in images is useful as anchor text if you decide to use an image as a link. — src: Google Search Central

Key takeaway

Image alt text helps with your page's overall SEO (it's part of the content after all) BUT it's main purpose is for people who can't see it to hear what it is (courtesy of a screen reader).

For ecommerce sites the alt tag is a great opportunity to have your site rank in an image search for your product. Similarly, for businesses like photographers, it's a great way to rank in an image search for your speciality:

  • ecommerce example: Front cover of 2022 wellness planner "It's okay not to do it all" by Typo
  • Photography site example: Children's Christmas photography with Santa hat prop, taken in Putney

As with any SEO activity, start with research though. Knowing the words your audience uses is the best way to start.

Looking for SEO help? Give us a ring on 0845 272 3534 or drop us a DM on instagram @reaperweb.