Missing Alt Text: The SEO Quick Win You're Ignoring

Alt text (short for alternative text) is a text description added to an image's HTML tag via the altattribute. It serves two purposes: it tells screen readers what an image shows, and it gives search engines context they can't get from pixels alone.

Most sites have dozens or hundreds of images missing alt text. Fixing them takes minutes per image, costs nothing, and delivers measurable improvements in both accessibility compliance and search visibility.

Why alt text matters

Accessibility is the primary reason

Screen readers — used by people who are blind or have low vision — rely on alt text to describe images. Without it, a screen reader either skips the image entirely or reads out the filename, which is usually meaningless (e.g., "DSC_0042.jpg" or "hero-banner-v3-final.png").

Web Content Accessibility Guidelines (WCAG) require alt text on all informative images. In many jurisdictions, this is also a legal requirement under disability discrimination laws.

SEO is a secondary benefit

Google can't see images the way humans do. Alt text is the primary signal Google uses to understand what an image depicts and whether it's relevant to a search query. Images with descriptive alt text can rank in Google Images — a traffic source most sites ignore. For e-commerce, Google Images drives purchase-intent clicks directly to product pages.

How to write good alt text

Be descriptive and specific

Describe what the image actually shows, not what you wish it showed. "A golden retriever catching a frisbee in a park" is useful. "Dog" is not. The test: could someone who can't see the image understand what it contributes to the page?

Keep it concise

Aim for one to two sentences, roughly 125 characters or fewer. Screen readers read alt text in a continuous stream — long descriptions become exhausting to listen to. If an image needs a longer explanation, use a caption or aria-describedby instead.

Don't stuff keywords

Writing alt text purely for search engines defeats the purpose and can trigger spam filters. "Buy cheap running shoes best running shoes discount running shoes" is not alt text — it's keyword spam. Describe the image naturally and relevant keywords will appear on their own.

Decorative images

Not every image needs a description. Purely decorative images — background patterns, spacer graphics, visual flourishes — should use an empty alt attribute: alt="". This tells screen readers to skip the image entirely. Omitting the alt attribute altogether is different and worse — the screen reader may fall back to reading the filename.

Common mistakes

• Using the filename as alt text."IMG_4392.jpg" tells nobody anything. CMS platforms sometimes auto-fill alt from the filename — always review it.
• Starting with "image of" or "picture of".Screen readers already announce the element as an image. Writing "Image of a sunset" results in the user hearing "Image: image of a sunset" — redundant and distracting.
• Making it too long. Alt text over 250 characters gets truncated by some screen readers and loses impact. If the image is complex (a chart, infographic, or diagram), put the detailed description in the surrounding text instead.
• Leaving the attribute off entirely. Missing alt is worse than empty alt="". Without the attribute, assistive technology has to guess, often reading a garbled URL path.

Finding missing alt text

Manually inspecting every image on a large site is tedious. An automated scanner can crawl your pages, flag every <img> tag missing the alt attribute, and report the exact page and image URL so you can fix them systematically. Prioritise images above the fold and on high-traffic pages first.