TECHNICAL · SEO GLOSSARY
Alt Text SEO
Optimisation of HTML `alt` attributes on images for search engine understanding and accessibility — covering descriptive alt text writing, keyword relevance, location signals for local SEO, alt text length best practices, and decorative image handling.
Definition
Alt text (alternative text) is the HTML `alt` attribute on `<img>` elements — serving as both an accessibility aid (screen reader narration for visually impaired users) and a search engine signal (the primary indexable text content for images). For SEO, alt text is the most important image optimisation factor — it is the text that Google indexes to understand what an image depicts, and it is the primary signal for ranking in Google Images. Alt text best practices: (1) **Descriptive accuracy**: describe what the image actually shows — "Couple exchanging rings at Edinburgh Castle chapel" not "wedding photo"; (2) **Keyword integration**: include relevant keywords naturally — the image context should make keyword inclusion natural rather than forced; (3) **Location signals**: for local businesses, including the location in alt text provides relevant local search signals — "traditional afternoon tea served in Edinburgh" on a restaurant image; (4) **Uniqueness**: every image in a gallery should have unique alt text — not the same template repeated with minor variations; (5) **Length**: typically 50-125 characters — long enough to be descriptive, short enough to remain focused; (6) **Decorative images**: purely decorative images (borders, dividers, icons used for styling) should use empty alt text (`alt=""`) — screen readers skip empty alt and Google understands the image has no meaningful content; (7) **File naming**: rename image files from camera output to descriptive slugs before uploading — "edinburgh-castle-wedding-ceremony.webp" provides both an alt text hint and a URL signal.
Why it matters for SEO
Alt text is the primary indexable signal for images — websites with comprehensive, descriptive alt text generate significantly more Google Images traffic than equivalent sites with empty or generic alt attributes. For photographer, ecommerce, and visual-content websites where images are core to the product or service, alt text optimisation is among the highest-ROI technical SEO tasks.
How DeepSEOAnalysis checks this
DeepSEOAnalysis checks all images on audited pages for alt attribute presence, flags empty alt text on non-decorative images, identifies generic or keyword-stuffed alt text patterns, validates alt text length, and includes alt text coverage in the overall technical audit score.
Useful tools and resources
GLOSSARY
Related terms
technical
ImageObject Schema
Schema.org `ImageObject` structured data for individual images — declaring image name, description, content URL, thumbnail, author, creator rights, and date created to support Google Images rich results and AI image search citation.
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Visual Search SEO
Optimisation for image-based search systems — Google Lens, Google Images, Pinterest visual search, and Bing Visual Search — covering ImageObject schema, alt text, image file naming, WebP format, and structured data for visual discovery.
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Google Lens SEO
Optimisation for Google Lens image recognition — ensuring images on business websites are well-indexed in Google Images with descriptive metadata, ImageObject schema, and visual context signals that help Lens identify and surface the content when users photograph related scenes or objects.
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Photographer SEO
SEO strategy for photography businesses — covering ImageObject schema for portfolio images, alt text optimisation for visual content, local search for wedding and portrait photographers, Core Web Vitals on image-heavy portfolio websites, and visual search via Google Lens.
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Image SEO
Optimising images for search — including descriptive alt text, semantic file names, correct dimensions, and next-gen formats — to improve rankings and Core Web Vitals.
Read definition →See how your site scores on Alt Text SEO.
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