Image Alt Text for SEO: The Complete 2026 Guide

Alt text serves as a textual substitute for an image. When Googlebot-Image crawls a page, it reads the alt text to understand what the image depicts. Google then matches that understanding against search queries. Alt text is the strongest single relevance signal for image ranking.

Google's 2025 image SEO documentation states: "Use descriptive alt text that accurately describes the image content and includes relevant context." This is not permission to keyword-stuff. It is a directive to write alt text that a search engine can confidently use as a description of the image.

Alt text is also used for:

• Image Pack ranking: Alt text directly influences whether an image qualifies for the Image Pack.
• Google Lens entity matching: Alt text helps Google's vision models confirm their entity predictions.
• Accessibility compliance: Screen readers render alt text audibly for visually impaired users.
• Failed image load fallback: Browsers display alt text when an image fails to load.

Good alt text follows a simple formula: subject + action/state + context + (optional) keyword.

Poor: "mug" Good: "Handmade ceramic coffee mug in blue glaze on a wooden table" Keyword-optimized: "Handmade ceramic blue coffee mug on rustic wooden table"

The keyword-optimized version keeps the keyword natural ("blue coffee mug") while maintaining readability. The difference from stuffing is subtle but important. "Blue coffee mug coffee mug handmade mug ceramic mug" is stuffing. It is unreadable and Google penalizes it through lower relevance scoring.

Google distinguishes between decorative and informational images. This distinction affects how you should write alt text.

Informational images (product photos, diagrams, infographics, screenshots): These convey content that cannot be expressed in text alone. Write detailed alt text that describes the content and its function. For a chart showing quarterly revenue, alt text should describe the trend, not just "quarterly revenue chart."

Decorative images (background textures, stylistic borders, spacer images): These add visual design but carry no content. Use alt="" (empty alt) to tell Google and screen readers to skip them. Do not omit the alt attribute entirely. An absent alt attribute causes some screen readers to read the image filename aloud.

Functional images (icons, logo links, buttons): Describe the function, not the appearance. A search magnifying glass icon should have alt="Search", not alt="Magnifying glass".

Standard img tag:

<img src="blue-mug.jpg" alt="Handmade ceramic blue coffee mug on rustic wooden table" />

Decorative image (empty alt):

<img src="background-texture.webp" alt="" role="presentation" />

Linked image (always describe the destination):

<a href="/products/blue-mug">
  <img src="blue-mug-thumb.jpg" alt="Handmade Ceramic Blue Coffee Mug - Product Page" />
</a>

Lazy-loaded image (maintain alt):

<img data-src="blue-mug.jpg" src="placeholder.jpg" alt="Handmade ceramic blue coffee mug" />

Alt text must survive lazy loading. Never strip alt text on the client side.

Keyword stuffing. Writing "buy coffee mug ceramic mug handmade mug coffee cup mug" as alt text. This reduces relevance scoring across all included keywords.

Missing alt on decorative images. Omitting the alt attribute entirely rather than using alt="". The attribute must be present but empty.

Duplicate alt text across images. Every image on a site should not have the same alt text. Each image is unique and should be described uniquely.

Overly short alt text. Single-word alt text provides insufficient context. Use at least 5-10 words for informational images.

Ignoring surrounding content. Alt text should complement the on-page content, not repeat it. If the paragraph already says "The handmade blue coffee mug features a ceramic glaze," the alt text can focus on visual details not in the text.

For multilingual setups, alt text must be translated per locale, not served with a single global alt attribute. Google evaluates alt text in the language of the page. Machine-translated alt text is acceptable if reviewed by a native speaker.

1. Verify every <img> element has an alt attribute (never omit it).
2. Confirm decorative images use alt="" not alt="decorative image".
3. Check informational images for descriptive (5+ word) alt text.
4. Remove duplicate alt text across the site.
5. Validate alt text keyword relevance without stuffing.
6. Test with a screen reader to confirm accessibility.
7. Review lazy-loading implementations to ensure alt text survives JavaScript execution.

Alt text is the single highest-impact, lowest-effort image SEO action you can take. It costs nothing, takes seconds to write, and directly signals relevance to Google. The trap is doing it poorly. Write for humans, optimize for search, and validate with tools. The formula is simple: describe the image as you would to a colleague who cannot see it.

1. Google. "Image SEO: A guide for web developers." Google Search Central Blog, 2025. https://developers.google.com/search/blog/2025/02/image-seo-guide
2. W3C. "Web Content Accessibility Guidelines (WCAG) 2.2: Non-text Content." W3C, 2025. https://www.w3.org/TR/WCAG22/#non-text-content
3. Google. "Google Images best practices." Google Search Central, 2025. https://developers.google.com/search/docs/appearance/google-images
4. Moz. "Alt Text: The Ultimate Guide." Moz Blog, 2025. https://moz.com/learn/seo/alt-text