Why image alt text is both an SEO and accessibility issue

Alt text serves two audiences: screen readers describing images to visually impaired users, and search engines understanding what each image depicts. Missing alt attributes fail accessibility audits (WCAG 2.1 Level A), get flagged by automated compliance tools, and remove a contextual ranking signal that Google uses for image search and AI Overviews.

Image search drives meaningful traffic. Google Images alone accounts for around 20% of all search queries. Every image without alt text is a missed chance to rank, both for image search and for the parent page's overall topical authority.

Decorative versus meaningful images

Not every image needs descriptive alt text. Decorative images (background patterns, divider lines, purely visual flourishes) should have empty alt attributes (alt=""). The empty attribute tells screen readers to skip the image entirely. Omitting the alt attribute completely is different and worse: screen readers read the file name aloud, which usually sounds like gibberish ("img- underscore-1234-dot-jpg").

For meaningful images, alt should describe what the image shows in the context of the page. A photo of a dog in a "dog breed guide" article should describe the dog and the breed. The same photo on a "pet adoption" page should focus on the adoption-relevant details.

Writing good alt text

Keep it under 125 characters. Screen readers cut off longer alt text. Be specific and contextual: "Golden retriever puppy chasing a tennis ball on grass" beats "Dog playing fetch". Avoid starting with "image of" or "picture of"; screen readers already announce that an image element exists.

Do not stuff keywords. Alt text full of target keywords reads unnaturally to screen readers and can trigger Google's keyword stuffing detection. Use the natural keyword if it describes what the image shows; do not force it.

For images of text (logos, infographics, screenshots with text), the alt should reproduce the text content of the image, not describe the image visually. "Quarterly revenue chart showing 23 percent growth" is better than "Bar chart with blue and gray bars".

What this checker actually looks for

Every img tag on the page. We extract the src and alt attributes for each, then categorize: missing alt entirely (worst), empty alt set explicitly (decorative, intentional), and alt with content. We report the first two as issues and provide the full list of all three for manual review.

We also flag suspiciously short alt text (under 5 characters that is not empty) and alt text that looks like a file name. Both usually indicate a CMS auto-filling alt with the image filename rather than someone writing real descriptions.

The distinction between a missing alt attribute and an empty one is the single most important thing to understand in the report. A missing attribute is a defect: the markup never accounted for accessibility at all, and a screen reader will fall back to reading the file path. An empty attribute is a deliberate decision that the image carries no information, which is correct for spacers, borders, and decorative flourishes. Our report keeps these in separate buckets so you are not chasing the wrong fix.

How to read the results and prioritize fixes

Start with the missing-alt count. That number is your accessibility and SEO debt in its rawest form, and every item in it should either get a real description or an intentional empty alt. Work through it image by image, deciding for each one whether it conveys meaning to the reader. If it does, write a description. If it does not, set alt to empty so the markup is explicit rather than accidental.

Next look at the flagged file-name-style and ultra-short alt text. These are technically present but worthless, and search engines treat "DSC 4892" or "image1" as no signal at all. They tend to cluster, because they come from the same broken upload workflow, so fixing the workflow usually clears dozens at once. Finally, review the longest alt strings for stuffing: anything that reads like a list of keywords rather than a sentence should be rewritten to describe the image plainly.

Weight your effort by visibility. Hero images, product photos, and in-content diagrams matter far more than a footer icon, both for users and for image search. A page can have a perfect alt-text score on trivial images and still fail the one image readers actually came to see, so judge the report against the page, not just the totals.

Alt text, captions, and title attributes are not the same

A frequent source of confusion is treating the alt attribute, the visible caption, and the title attribute as interchangeable. They are not. Alt text is the screen-reader and search-engine description that appears only when the image cannot be seen. A caption is visible text below the image that everyone reads, and it complements rather than replaces alt. The title attribute produces a hover tooltip that most users never see and screen readers handle inconsistently, so it should never be relied on for accessibility.

The practical rule is that every meaningful image needs alt; a caption is a bonus when context helps all readers; and the title attribute is optional and low value. Do not duplicate the caption verbatim into the alt, because a screen-reader user would then hear the same sentence twice. Write the alt to describe the image and let the caption add the context, credit, or commentary that sighted readers benefit from.

Common image alt mistakes

WordPress sites often have alt text auto-filled from the image filename. "DSC_4892.jpg" becomes alt="DSC 4892", which is useless. Configure your media library to require alt text on upload, or run a sweep updating alt fields for all existing images.

Lazy-loaded images sometimes appear without alt because the alt is set after page render via JavaScript. Search engines and accessibility tools may evaluate the page before that JavaScript runs. Use native loading="lazy" with alt set in the initial HTML rather than JS-injected.

Background images set via CSS do not have alt text at all. If the background image conveys important information, it should be a real img element with alt, not a CSS background. Background should be reserved for decorative imagery.

Image alt and AI search

AI search tools rely on alt text to understand image content, especially for queries that might surface images in answers ("what does X look like", "show me Y"). Pages with descriptive alt text more reliably surface their images in AI image cards and feature them in citations.

Alt text is also a natural signal for content quality. A page with 20 images, all with thoughtful alt text, signals to crawlers that this is a carefully edited piece of content. The same page with 20 missing-alt images signals templated or auto-generated content.

As multimodal models become the norm, the relationship between the alt text and the surrounding paragraph matters more than the alt text in isolation. An engine that reads "as the chart below shows" and then finds an image with descriptive alt confirming the same figure treats the claim as better supported. Alt text that contradicts or has nothing to do with the nearby prose is a small but real trust signal in the wrong direction. Write alt that reinforces the point the image is there to make.

Alt text and the rest of the image SEO picture

Alt text is the highest-leverage image fix, but it is not the only one, and this checker is the natural first step in a broader pass. Once alt is handled, the descriptive file name (cycling-helmet-blue beats DSC_4892), a sensible width and height to prevent layout shift, a modern format like WebP or AVIF, and lazy loading for below-the-fold images all compound the same goal: images that load fast, rank in image search, and stay accessible.

Think of alt as the meaning layer and the others as the delivery layer. The meaning layer is what wins image-search and AI-citation visibility; the delivery layer is what keeps Core Web Vitals healthy so those images do not drag the whole page down. Both matter, but a fast image no one can understand and a well-described image that tanks your layout score each leave value on the table.

Building alt text into your workflow

The durable fix is upstream of any single page. Configure your CMS or media library to require an alt field on upload, and make the default empty rather than the file name so nothing slips through as gibberish. For teams, add "every meaningful image has descriptive alt" to the publishing checklist next to title and meta checks.

For existing libraries with hundreds of legacy images, batch the work by template and by page importance. Fix the homepage, top landing pages, and best-performing articles first, since those carry the most traffic and the most images people actually see. Then sweep the long tail. After each batch, re-run this checker on a sample of pages to confirm the missing-alt count is dropping and no new file-name-style alt is creeping back in from the upload flow.