Images with Descriptive Alt Text

TL;DR — Multimodal AI engines process images directly. Text-only models use alt attributes as additional text signals. Images with meaningful alt text add entity mentions and contextual cues that reinforce a page's topic relevance.

Why Images and Alt Text Matter for AI Engines

Multimodal AI engines — GPT-4V, Gemini, Claude — process images as part of their content analysis. When a page includes a chart or diagram, the model can extract information from the visual itself. But even for text-only models that don't directly process images, the alt attribute functions as additional body text — another opportunity to mention key entities and reinforce the page's topic.

Pages with zero images are flagged by some quality assessment signals as "thin content" — a page that makes no visual effort to illustrate its claims. This heuristic, borrowed from traditional SEO, has carried over into AI engine quality signals.

The alt text itself matters as much as the presence of images. An alt attribute that describes both what is shown AND why it's relevant to the topic adds meaningful entity reinforcement: alt="Line chart showing 38% improvement in AI citation rate after adding FAQPage schema" contributes three entity signals (metric type, percentage, schema type) that would otherwise require a full sentence to convey.

How to Implement

• At minimum 1 relevant image per major section
• Alt text should describe what's in the image AND its relevance to the topic
• Use loading="lazy" for below-fold images to improve Core Web Vitals
• Provide width and height attributes to prevent cumulative layout shift

<img
  src="/charts/geo-citation-improvement.png"
  alt="Bar chart showing 38% higher AI citation rate on pages with FAQPage schema vs pages without"
  width="800"
  height="450"
  loading="lazy"
/>

Common Mistakes

• Empty alt="" on informational images — correct only for purely decorative images; informational images need descriptive alt text
• Filename as alt text — alt="image123.jpg" or alt="screenshot" adds no entity signal
• Stock photos with generic alt text — "businesspeople shaking hands" adds no topical relevance; use alt text that connects the image to the page topic

Sources

• MDN — The Image element alt attribute
• Google Image SEO best practices