Image Alt Text for SEO: Rules, Examples and Common Mistakes

Image alt text is the short written description attached to an image in your HTML. It is read aloud by screen readers, shown when an image fails to load, and used by search engines to understand what an image shows. Good image alt text makes your site more accessible and gives your images a better chance of appearing in image search; poor alt text, or none at all, wastes both. This guide sets out the rules, gives real examples for different image types, and covers the mistakes that show up most often.

This guide is part of our complete website SEO audit guide, which walks through every step of auditing a small site.

What image alt text is and why it matters

Alt text lives in the alt attribute of an <img> element:

<img src="blue-ceramic-mug.webp" alt="Handmade blue ceramic mug on a wooden table">

It serves three purposes:

• Accessibility. People using screen readers hear the alt text in place of the image. Without it, they may hear the file name, or nothing at all, and miss information everyone else can see.
• Fallback. If an image fails to load because of a slow connection or a broken file, browsers display the alt text in its place.
• Search. Search engines cannot fully “see” images the way people do. Google’s image SEO best practices name alt text as one of the signals it uses, together with the surrounding text, captions and file names, to understand an image and the page it sits on.

Accessibility comes first. If you write alt text to help someone who cannot see the image, you will almost always also write good alt text for search.

The rules of good image alt text

1. Describe what matters in context. The same photo might need different alt text on different pages. A photo of a chef in a kitchen could be “Head chef plating a risotto” on a restaurant page and “Stainless steel commercial kitchen with gas range” on a kitchen fitter’s page.
2. Be specific and concise. Aim for a sentence or a short phrase. There is no official character limit, but roughly 125 characters or fewer keeps it easy to listen to.
3. Do not start with “image of” or “picture of”. Screen readers already announce that it is an image.
4. Include a keyword only when it genuinely describes the image. If your page is about blue ceramic mugs and the photo shows one, saying so is accurate. Listing every keyword you want to rank for is not.
5. Include text that appears in the image. If an image contains important words, such as a sign, a sale banner or a quote graphic, put those words in the alt text.
6. Use empty alt text for decorative images. Purely decorative images should have alt="" so screen readers skip them. Leaving the attribute out entirely is not the same thing.
7. Do not repeat the caption word for word. If a caption already describes the image, the alt text can be shorter or add detail the caption leaves out.

The W3C’s images tutorial includes a useful decision tree for working out which type of alt text an image needs.

Image alt text examples by image type

Different kinds of images call for different approaches:

Functional images

When an image is a link or a button, the alt text should describe what happens when it is clicked, not what it looks like. A magnifying glass icon that submits a search form should have alt text like “Search”, not “Magnifying glass”.

Complex images

Charts, infographics and diagrams carry more information than a short phrase can hold. Give them a brief alt text that identifies the image and its main point, then explain the details in the surrounding text or a data table so everyone can access them.

Common image alt text mistakes

• Missing alt attributes. The most common image alt text problem by far, especially on older posts and images uploaded in bulk.
• File names as alt text, such as “IMG_4821.jpg” or “final-v2-crop”.
• Keyword stuffing, like “cheap plumber London plumber emergency plumber London”. This is unhelpful for screen reader users and offers no benefit in search.
• The same alt text on every image, often the page title copied across a whole gallery.
• Describing decorative images in detail, which forces screen reader users to listen to irrelevant content.
• Important text baked into images with no alt text, such as an opening hours graphic or a promotional banner.
• Alt text that contradicts the image after the photo has been swapped but the description was not updated.

In WordPress, note that alt text set in the Media Library is generally used when the image is first inserted. If you update it later in the library, images already placed in posts may keep their old alt text, so check the block or page builder settings too.

How to audit image alt text on your website

Most sites have far more images than anyone remembers uploading, and image alt text is rarely reviewed after publishing, so finding the gaps is the hard part. A practical approach:

1. Crawl your key pages. The LiteScroll SEO Crawler scans up to 25 pages free and flags image alt tags along with titles, meta descriptions and headings. Download the CSV to see which pages have images without alt text.
2. Prioritise. Start with your homepage, product and service pages, and the posts that bring in the most traffic.
3. Classify each image. Is it informative, functional, complex or decorative? That decides what kind of alt text it needs.
4. Write and update. Edit the alt text in your CMS for each image placement, not just in the media library.
5. Re-crawl to confirm. Run the crawl again to make sure the gaps have closed.

For one-off checks while you are editing, open the page in Chrome and right-click an image, then choose Inspect to see its alt attribute. If you also use the free LiteScroll SEO Inspector extension for metadata and headings, you can review a page’s on-page basics and its image alt text in the same short session before moving on to the next page.

If you are checking alt text as part of a wider review, our guide to running a 25-page SEO audit shows how to fit it in with the other on-page checks, and the small business SEO audit checklist lists it alongside everything else worth reviewing each year.

Image alt text checklist

• Every informative image has descriptive, specific alt text.
• Alt text describes the image in the context of the page.
• No “image of” or “picture of” at the start.
• Keywords appear only where they accurately describe the image.
• Linked images and buttons describe their function.
• Text inside images is repeated in the alt text.
• Decorative images use alt="".
• Charts and infographics are explained in the surrounding text.

Alt text sits alongside other structural details that help people and search engines understand a page. Our guide to H1 tags and heading structure covers the other half of that picture.

Key takeaways

Write image alt text for people first: describe what an image contributes to the page in a short, specific phrase, use empty alt for decoration, and describe function for links and buttons. Do that consistently and the search benefits follow naturally. Start by crawling your most important pages, fix the missing and weak alt text you find, and make alt text part of your publishing routine from now on. For more lightweight SEO tools and guides, visit LiteScroll.com.