Alt text: How to make meaning obvious to human and machines

Your images are invisible to the systems deciding whether to cite your content.

AI search doesn’t see screenshots, charts, or product photos in your web content; it reads the alt text you wrote (or didn’t write, or auto-generated and forgot about). When that description is vague, generic, or missing entirely, you’ve handed Google and ChatGPT a blank space where proof should be. They move on. Your competitor with clear, specific alt text gets the citation.

But here’s the thing: Alt text that works for AI also works for humans using screen readers, improves image SEO, and keeps you compliant with accessibility standards. The same specificity that helps a blind user understand a dashboard screenshot also helps a large language model pull the right details into a summary.

This guide shows you how to write alt text that both people and machines can use:

• Build an alt text standard that eliminates ambiguity and boosts retrieval.
• Connect image descriptions to the claims AI systems need to verify.
• Set up workflows so that alt text gets written correctly once, and at creation time.
• Audit what you have, fix what matters, and prove the impact.

Let’s start with what alt text does and why most teams get it wrong.

Best practices for writing alt text

High-quality alt text states the image’s purpose in context using precise entities and actions, eliminating ambiguity so AI systems can interpret and cite the right details.

I’ve found that most alt text fails because writers treat it like a Mad Libs game: “[Type of image] showing [vague description].” Chart showing data trends. Screenshot of the interface. These descriptions tell you nothing.

So what’s the fix? A repeatable pattern: Subject + Action + Attribute + Purpose

Here’s a clear alt text example:

Examples of weak vs. strong alt text

Weak alt text	Strong alt text
"Dashboard screenshot"	"Siteimprove Content Quality dashboard showing 42 readability issues flagged across 200 blog posts"
"Chart showing growth"	"Line chart comparing organic traffic growth: Site A increased 40% while Site B remained flat from Q1 to Q4 2024"

How much detail to include

This depends on what the image is doing:

• Product images: Model numbers, colors, visible features (e.g., “Logitech MX Master 3S mouse in graphite with side scroll wheel”)
• Charts: Trends and key data points (e.g., “Bar chart showing email open rates: Monday 22%, Wednesday 31%, Friday 18%”)
• Screenshots: Name the interface and highlight what matters (e.g., “WordPress editor with Siteimprove extension flagging broken link in paragraph 3”)
• Complex images: Break down multiple data points or relationships (e.g., “Venn diagram showing overlap between SEO, accessibility, and UX with 23% of surveyed sites meeting all three criteria”)

Use specific entity names in your image description whenever the image proves a claim. If your article recommends Siteimprove for WCAG tracking, say “Siteimprove Accessibility module” in the alt text, not “accessibility tool.” AI systems match entities across your content. If you break that connection, you break retrieval.

What kills alt text quality

Skip these:

• Keyword stuffing: “Best enterprise SEO platform tools software dashboard” (reads like spam)
• Generic boilerplate: “Company dashboard” repeated across 50 images
• Filler phrases: “Image of” or “picture showing” (the alt attribute already signals it’s an image)
• Repeating adjacent copy word-for-word (annoying for screen reader users)

Alt text works when it’s specific, contextual, and connected to the claims your page makes.

The impact of alt text on AI search and accessibility

Alt text converts images into machine-parsable signals that power accessibility, image indexing, and AI grounding, improving retrieval precision and increasing citation eligibility.

I’ve seen teams obsess over meta descriptions and title tags while ignoring alt text entirely. Then they’re shocked when their competitor’s less-detailed article gets cited in AI overviews. The difference? Their competitors’ screenshots had alt text that AI systems could parse, verify, and pull into summaries.

Alt text does three things simultaneously, and most teams only think about one of them.

How alt text improves accessibility

Screen readers announce alt text to blind users navigating your site. If you write “Siteimprove dashboard” instead of “Siteimprove Accessibility score showing 87/100 with 12 high-priority issues,” you’ve told them an image exists, but not what it shows. That’s like handing someone a blank page and saying, “There’s important information here.”

Good alt text gives screen reader users the same information sighted users get from the image, without duplicating the surrounding copy. If your paragraph explains that Springfield Clinic reduced accessibility errors by 60 percent, your screenshot alt text should specify what’s visible: “Springfield Clinic accessibility dashboard showing error count dropping from 847 to 339 over six months.”

How alt text powers image SEO

Every search engine indexes alt text to understand what images show and match them to queries. When someone searches for “accessibility dashboard example” or “WCAG compliance tracking interface,” your images can appear in Google Images results, but only if your alt text naturally includes those specific terms.

According to research from Stanford's Accessibility team, images with descriptive alt text significantly outperform those with generic descriptions in both accessibility metrics and search visibility. The same specificity that helps a blind user also helps Google decide if your image answers the query.

How alt text enables AI grounding and citation

Here’s where AI search gets interesting. Language models can’t see images; they read the alt text and use it to:

• Disambiguate meaning: Is that dashboard tracking SEO, accessibility, or content quality? Alt text tells them.
• Resolve entities: Does this screenshot show Siteimprove, Google Analytics, or a generic tool? Specific names matter.
• Verify claims: If your copy says, “most common errors include missing headings,” does your screenshot back that up? AI will check the alt text to find out.

Computer vision models may analyze images, but they still rely on alt text to confirm context and meaning.

Research from IEEE on AI retrieval systems shows that precise image descriptions improve AI’s ability to extract and cite accurate information. Vague alt text creates ambiguity, and when AI systems can’t verify a claim, they cite someone else.

The payoff shows up in impressions, clicks, and assisted conversions. Images with high-signal alt text get pulled into AI summaries, show up in image search results, and help your pages rank for visual queries your competitors miss.

Tools and techniques for testing alt text quality

Alt text quality is enforceable: Automated audits and human QA catch missing, duplicate, and low-signal descriptions so AI systems retrieve the correct asset and cite the correct page.

This means you need a workflow that flags problems at scale, not a manual review of 10,000 images.

Run automated audits first

Start with tools that crawl your site and surface the obvious failures, such as:

• Missing alt text: Images with no alt attribute at all
• Empty alt text on informative images: Images marked decorative (alt=“”) that shouldn’t be
• Duplicate descriptions: The same generic phrase (e.g., “dashboard screenshot”) is used across 50 images
• Boilerplate patterns: Alt text that’s just the filename (e.g., “IMG_2847.jpg”) or keyword spam

Most CMS platforms and accessibility checkers (including Siteimprove's QA tools) automatically flag these. The key is prioritizing fixes by impact: High-traffic pages, template components, and images supporting key claims get fixed first.

Add human QA for context and precision

Automated checks catch structural problems. Human review catches lazy descriptions.

Your QA checklist:

• Does the alt text include specific entity names mentioned in the surrounding copy?
• Can someone understand the image’s purpose without seeing it?
• Does it support a claim on the page, and is that connection clear?
• Would this description help an AI system verify the content?

According to recent research on alt text generation, human-validated descriptions consistently outperform auto-generated ones for both accessibility and retrieval tasks. AI can suggest image alt text, but you still need someone to check that “accessibility dashboard” becomes “Siteimprove Accessibility module showing WCAG 2.2 compliance score.”

Track coverage and quality trends over time. Report them to the SEO, Accessibility, and Content teams so everyone can see the progress.

Legal and compliance considerations for alt text

Alt text is a documented control for accessibility conformance and audit readiness, and it strengthens AI citation trust by aligning image descriptions with verifiable on-page evidence.

Most teams ignore alt text until Legal forwards an accessibility complaint. Then it’s crisis mode, retrofitting 10,000 images while an auditor waits for your WCAG conformance report.

WCAG 2.1 Success Criterion 1.1.1 requires alternative text for all non-text content. Section 508 extends this to federal agencies and contractors, though many enterprises adopt it as an internal standard anyway. Missing or vague alt text creates legal risks and audit gaps you’ll have to explain later.

What compliance evidence looks like:

Alt text compliance evidence to track

What to track	Why it matters
Coverage rates	Percentage of images with alt text by template and content type
Exception logs	Decorative images intentionally marked null (alt="") with justification
Remediation queue	High-priority fixes assigned to owners with deadlines

Consistency matters beyond compliance. When your alt text descriptions contradict the surrounding copy or use different entity names for the same thing, you’ve created ambiguity. Auditors flag it. AI systems skip citing it. Fix it once in templates and governance, not image-by-image during an emergency remediation sprint.

Integrate alt text into a unified content strategy

Alt text belongs in your content operating model: Clear ownership, templates, and governance standardize image descriptions so AI systems interpret your content consistently across the site.

Alt text fails when it’s an afterthought. Someone uploads an image at 4:45 p.m., types “screenshot,” and hits publish. Multiply that across 50 content creators, and you’ve got chaos; half your images have no alt text, while the other half have garbage.

The fix is to make alt text impossible to skip.

Operational changes that stick:

• Assign ownership based on image source: Have the Design team handle component library images, the Content team handle blog/article images, and the Product team handle feature screenshots.
• Require alt text in CMS workflows: Make the field mandatory before publishing, with no exceptions.
• Build alt text into templates: Pre-populate patterns, such as “Siteimprove [Module Name] showing [specific data/feature]”, for creators to customize.
• Create review gates: Check alt text against page claims during content approval.

When alt text is written at asset creation, not at publish time, quality improves and velocity doesn’t suffer. Your entity names stay consistent, your descriptions match page context, and AI systems can map images to claims without guessing.

Governance isn’t bureaucracy. It’s the difference between scalable quality and emergency fixes every audit cycle.

Make alt text work before the audit does

Alt text quality drives accessibility compliance, image SEO, and AI citation eligibility simultaneously. Write specific, context-driven descriptions, and you get screen reader clarity, search visibility, and verifiable evidence that AI systems can cite.

The teams that win treat alt text as infrastructure, not audit cleanup. They assign ownership, enforce CMS standards, and fix templates before publishing thousands of images that are vague.

Start with high-traffic pages. Audit what’s missing or duplicated. Prioritize images that support key claims. Fix those, document coverage gains, then scale.

Your next AI citation depends on whether language models can parse your screenshots and connect them to claims. Your next audit depends on whether you built quality in from the start.

Ready to automate alt text governance? Request a demo to see how Siteimprove can scale quality checks across your entire site.