Guide · Practitioner
Image Alt Text and Multimodal AI Search
Good alt text describes what an image shows and why it matters on the page, in plain words, without keyword stuffing. Google says alt text is the most important attribute for image metadata, and that it uses alt text alongside computer vision and the page's content to understand images (Google). Google's generative AI features can include images, and it points site owners to its image SEO guidance (Google).
Facts are from Google Search Central and W3C WAI, accessed 30 Oct 2026. Recommendations marked "our view" are interpretation.
On this page
- What does Google say about alt text?
- How do you decide what alt text to write?
- What makes alt text good?
- What about filenames, titles and captions?
- How should charts and diagrams be described?
- What are before-and-after examples?
- Do images on product pages need anything extra?
- How do you audit alt text at scale?
- Should you use AI to write alt text?
- Which pitfalls should you watch for?
- Why does alt text help beyond search?
- How do multimodal systems use images?
- Checklist
- From MentionX data: why the surrounding text still matters
- Worked example: Ledgerline fixes alt text on its product tour
- Which images need alt text?
- How long should alt text be?
- How do you write alt text for screenshots?
- How do you write alt text for product photos?
- How do you handle images with text in them?
- How do you build alt text into your workflow?
- How do you check alt text quality?
- What about images in PDFs and emails?
- How does alt text relate to accessibility law?
- Who should write alt text?
- Common questions
- Related
- Sources
Checked on 31 October 2026. "Our view" marks MentionX opinion. Ledgerline is a fictional company used for illustration.
What does Google say about alt text?
From Google's image SEO documentation (Google):
- Alt text is the most important attribute for providing image metadata.
- Google uses alt text together with computer vision algorithms and the page content.
- Alt text also helps people using screen readers.
- Write useful, information-rich content that uses keywords appropriately and is in context.
- Avoid filling alt attributes with keywords, which is a bad user experience and may cause your site to be seen as spam.
Google's example of good alt text is alt="Dalmatian puppy playing fetch", compared with an empty alt, a single keyword, or a string of keywords.
How do you decide what alt text to write?
W3C's alt decision tree works through questions (W3C):
| Situation | What to do |
|---|---|
| Image contains text also shown nearby | Empty alt |
| Image contains text not shown elsewhere | Put the text in alt |
| Image is a link or button | Describe the destination or action |
| Image adds meaning | Describe the meaning briefly |
| Image is purely decorative | Empty alt (alt="") |
W3C's images tutorial also covers complex images such as charts, which need a longer description elsewhere on the page (W3C).
What makes alt text good?
Our view:
- Describe what's shown and why it's there, in one sentence
- Be specific: "Approval screen showing three pending invoices" beats "screenshot"
- Skip "image of" or "picture of"; screen readers announce images
- Keep it concise; put long explanations in captions or text
- Use the page's language
What about filenames, titles and captions?
Google recommends descriptive filenames, titles and captions, and says it extracts information about an image from surrounding text, including captions (Google). Our view: invoice-approval-mobile.png is better than IMG_4821.png, and a caption that explains a chart's takeaway is often the most quotable text about it.
How should charts and diagrams be described?
Our view: use short alt text naming the chart and its main finding, then give the data in a nearby HTML table or text. W3C classes these as complex images that need a long description (W3C). A chart whose data exists only as pixels is hard for readers and engines to use accurately.
What are before-and-after examples?
Fictional examples:
| Before | After |
|---|---|
alt="" on a product photo | alt="Grey wool running shoe, side view" |
alt="shoe shoes running shoes best shoes" | alt="Grey wool running shoe, side view" |
alt="chart" | alt="Bar chart: support tickets fell 40% after launch" plus data table |
alt="logo" linking home | alt="Acme home" |
alt="Decorative swirl" | alt="" |
The 40% is fictional.
Do images on product pages need anything extra?
Our view: yes, alt text plus structured product data and Merchant Center feeds, which Google's AI optimization guide mentions for shopping visibility (Google). Use several real photos from different angles with distinct alt text.
How do you audit alt text at scale?
- Crawl your site and export images with their alt attributes.
- Flag missing alt, keyword-stuffed alt and duplicates.
- Prioritise templates (product, blog, docs) and fix at the source.
- Spot-check decorative images use empty alt.
- Add alt text requirements to your CMS upload workflow.
Should you use AI to write alt text?
Our view: AI tools can draft descriptions at scale, but they can miss context and misidentify products. Review drafts, especially for product details, people and charts. Google's guidance on AI-generated content focuses on accuracy and quality rather than how content is made (Google).
Which pitfalls should you watch for?
- Missing alt on informative images
- Keyword lists instead of descriptions
- Same alt text on every image in a gallery
- Text baked into images with no text alternative
- Charts with no data in text
Why does alt text help beyond search?
Alt text is first an accessibility feature. People using screen readers rely on it to understand images, and Google notes it helps them (Google). Our view: writing for those readers first produces the clear, specific descriptions that also help search and multimodal systems. If an image tells a screen reader user nothing, it probably tells an engine little too.
How do multimodal systems use images?
Our view: systems that analyse images directly can identify objects, but they can't know your product name, the context of a screenshot or why an image is on the page. Alt text, captions and nearby text supply that context. Google confirms it combines computer vision with page content and alt text (Google), so the text around an image still matters.
Checklist
- Informative images described in one sentence
- Decorative images use
alt="" - No keyword stuffing
- Descriptive filenames and captions
- Charts have data in text
- CMS requires alt on upload
From MentionX data: why the surrounding text still matters
Method. Read-only aggregate queries over MentionX scans from 22 August to 29 October 2026 (UTC): 2,217 engine runs (2,154 completed) across 18 anonymised projects and six engines.
Multimodal systems can read images, but engines still cite pages, and the MentionX sample shows which page types are cited most:
| Cited URL type | Share of 9,750 citations |
|---|---|
| Blog or article | 19.6% |
| Homepage | 10.0% |
| Review page | 2.7% |
| Docs | 2.6% |
| Pricing | 1.9% |
| Wikipedia | 1.6% |
Engines also differ in how often they cite any source:
| Engine | Brand mentioned | Answers with no citations |
|---|---|---|
| Gemini | 47.3% | 50.7% |
| OpenAI | 42.9% | 30.2% |
| Perplexity | 31.5% | 4.1% |
| AI Mode | 31.3% | 12.6% |
| Copilot | 26.0% | 47.0% |
| DeepSeek | 24.0% | 99.0% |
Our view: treat alt text as part of the page's text. Engines that cite often are citing pages, so an image's meaning should be clear from the alt text, caption and nearby text, not only from the pixels.
Limits. A convenience sample of mostly B2B software projects, run through engine APIs, which can behave differently from the consumer apps. Perplexity, Copilot and DeepSeek figures come from a single day (26 October 2026), so treat them as a snapshot, not a trend.
Worked example: Ledgerline fixes alt text on its product tour
Ledgerline is a fictional accounts-payable tool. Figures are illustrative.
Ledgerline's product tour page has twelve screenshots. Most have alt text such as "screenshot1" or are empty. One chart, showing the stages of invoice approval, has no description at all.
A content designer writes alt text for each screenshot, describing what it shows, such as "Approval rules screen with two approvers set for invoices over a set amount". Decorative background images get empty alt text so screen readers skip them. The chart gets a short summary in the alt text and a full description in a caption below. The team also renames image files to describe their content.
Which images need alt text?
Every image that carries meaning needs alt text: screenshots, product photos, diagrams, charts and photos that support the text. Decorative images, such as background patterns and dividers, should have empty alt text so assistive technology skips them. Logos usually need the company name. Images used as links need alt text that describes where the link goes.
How long should alt text be?
Short enough to read easily, usually a sentence. There's no strict limit, but screen reader users hear the whole thing, so long descriptions become tiring. If an image needs more explanation, put it in a caption or the main text and keep the alt text brief.
How do you write alt text for screenshots?
Say what screen it is and what it shows that matters for the page. Name the feature and the key detail, such as a setting or a result. Don't describe every button. If the screenshot shows a step, link the alt text to the step in the text.
How do you write alt text for product photos?
Describe the product, its colour, material or other visible features that a buyer cares about, and the angle if there are several images. Use the product name. Avoid repeating the same alt text across every photo in a gallery.
How do you handle images with text in them?
If an image contains text, such as a quote or a banner, include the text in the alt text or, better, in the page itself. Text in images is harder for everyone to read and search, so use real text where possible.
How do you build alt text into your workflow?
Make alt text a required field in your CMS where you can. Add it to your content checklist and editorial review. Brief designers and writers together, so whoever knows why the image is there writes the description. Check new pages before publishing.
How do you check alt text quality?
Sample pages each quarter and review alt text against a short rubric: is it present where needed, accurate, concise and useful in context? Use a screen reader on one or two key pages to hear how they sound. Our view: a quick check by someone outside the team often catches the most problems, because they don't already know what the images show.
What about images in PDFs and emails?
The same principles apply. Add alternative text to images in PDFs using your authoring tool, and in marketing emails, where many readers see images blocked by default. Clear alt text makes those messages usable before images load.
How does alt text relate to accessibility law?
In many regions, websites must meet accessibility standards that include text alternatives for images. Check what applies to you with your legal team. Good alt text helps you meet those standards and improves the experience for all users.
Who should write alt text?
The person who chose the image usually knows best why it's there, so ask writers and designers to write it together. For large image libraries, give editors a short style guide with examples of good and poor alt text, and review a sample regularly.
Common questions
Does alt text help rankings? Google says it helps it understand images; it's one signal among many.
Should I put keywords in alt text? Only if they describe the image accurately; avoid stuffing.
Is empty alt text a problem? Not for decorative images; it tells assistive technology to skip them.
Related
Sources
- Google, Image SEO best practices; AI optimization guide; Using generative AI content
- W3C WAI, An alt decision tree; Images tutorial
All accessed 30 Oct 2026.
Questions
Does alt text matter for AI search?
Google says alt text is the most important attribute for providing image metadata and that it uses alt text with computer vision and page content. Its AI features can include images, so the same guidance applies.
Should every image have alt text?
Every img element needs an alt attribute, but decorative images should use an empty one (alt=""), per W3C's guidance.
Can I put keywords in alt text?
Describe the image naturally. Google warns that filling alt attributes with keywords is a bad user experience and may cause the site to be seen as spam.