Image Alt Text for SEO: How to Write It and Why It Matters

Alt text — the alternative text attribute added to HTML image tags — is one of the most consistently overlooked on-page SEO elements. Most sites either skip it entirely, fill it with generic descriptions, or stuff it with keywords in a way that helps no one. Getting alt text right is straightforward, takes minimal time per image, and has a measurable impact on both accessibility and search visibility.

What Alt Text Is and What It Does

Alt text is the text that appears in place of an image if the image fails to load. It is also read aloud by screen readers for visually impaired users, and it is one of the primary ways search engines understand what an image contains.

Google cannot see images the way humans can. It reads the alt text, surrounding copy, filename, and page context to understand what an image depicts. Descriptive, accurate alt text helps Google classify your images correctly for image search, understand the relevance of your page content, and better assess the context of your topics overall.

From an accessibility standpoint, alt text is not optional — it is required under WCAG 2.1 accessibility guidelines. Sites without proper alt text fail basic accessibility standards, which has legal implications in many jurisdictions and practical implications for the significant portion of users who rely on assistive technology.

The Rules for Writing Good Alt Text

Be Specific and Descriptive

Describe what is actually in the image clearly and concisely. "Man using laptop" is less useful than "Marketing professional reviewing SEO analytics dashboard on laptop". The more specific you are, the more useful the alt text is for both users and search engines.

Include Your Target Keyword — Where It Fits Naturally

If your page targets a specific keyword and the image is directly related to that topic, include the keyword in the alt text naturally. If you are writing a post about meta description generators and the image shows a screenshot of the tool interface, "AI meta description generator tool interface showing three generated variants" is both descriptive and relevant.

The key phrase is "where it fits naturally." Do not force keywords into alt text that do not relate to the actual image content. A stock photo of a person typing at a keyboard does not need "best SEO tools 2026" in its alt text — that is keyword stuffing, which Google penalises.

Keep It Under 125 Characters

Screen readers typically cut off alt text after 125 characters. Keep descriptions concise while still being specific. If an image is complex — like an infographic with multiple data points — consider providing a longer description in the body text beneath the image and using a shorter summary in the alt text.

Use Empty Alt Text for Decorative Images

Decorative images — background patterns, dividers, purely aesthetic elements — should have empty alt text (`alt=""`). This tells screen readers to skip the image entirely, which is the correct behaviour for content that conveys no meaningful information. Adding placeholder text like "decorative divider" to these images adds noise without value.

Do Not Start With "Image of" or "Photo of"

Screen readers already announce that the element is an image. Starting your alt text with "Image of a laptop showing..." is redundant — just start with the description: "Laptop showing..."

Alt Text for Different Image Types

Screenshots

Screenshots of interfaces, dashboards, or tools should describe what is shown, focusing on what is most relevant to the surrounding text. "Google Search Console Coverage report showing 245 indexed pages and 12 errors" is far more useful than "screenshot".

Infographics

Infographics pack large amounts of data into a single image. Alt text cannot fully capture a complex infographic, so use alt text for the key takeaway and provide a full text version of the infographic data elsewhere on the page. "Infographic: 7 key SEO statistics for 2026, including that 60% of searches are zero-click" gives screen reader users the core message without attempting to replicate the entire graphic.

Charts and Graphs

Describe the chart type, what it measures, and the main finding. "Bar chart showing organic traffic growth from 5,000 to 23,000 monthly sessions between January and December 2025" gives screen reader users the context to understand what the chart conveys.

Product Images

For ecommerce, alt text should describe the product specifically — colour, model, key features. "Nike Air Max 270 running shoes in black and white, size 10, side view" is useful both for accessibility and for image search, where users frequently search by product description.

Writing Alt Text at Scale

For sites with large image libraries — ecommerce stores, content publishers, stock photo sites — writing alt text manually for every image is impractical. The free AI Alt Text Generator at SEOAITools.io addresses this at scale. Describe your image and the context it is appearing in, and the tool generates three SEO-optimised alt text variants, each under 125 characters, with your keyword incorporated naturally where appropriate.

This makes it feasible to systematically work through a backlog of images with missing or weak alt text — one of the highest-ROI technical SEO tasks available for most sites.

Auditing Your Current Alt Text

To audit your existing alt text, crawl your site with Screaming Frog or a similar tool and export the image report. This will show every image on your site alongside its current alt text. Look for: images with completely empty alt text (excluding intentionally decorative images), images with generic alt text like "image" or "photo", images where the alt text is just the filename (e.g. "IMG_4392.jpg"), and images with suspiciously long alt text that may be keyword-stuffed.

Prioritise fixing alt text on: images on your highest-traffic pages, product images on pages with commercial intent, and images that are likely to appear in image search for your target keywords.

The Compound Benefit of Good Alt Text

Image search drives meaningful traffic — particularly in certain industries like food, fashion, travel, and design. But even on sites where image search is not a primary traffic channel, thorough alt text contributes to overall page quality signals, accessibility compliance, and the comprehensive understanding that helps Google assess topical authority.

It is a small investment per image and a compounding asset over time. Every image you describe properly today strengthens your site's SEO foundation permanently.