Image alt text is one of the most overlooked opportunities in on-page SEO. Every image on your website should have descriptive, well-written alternative text that helps search engines understand the image content and enables visually impaired users to experience your pages fully. Despite its importance, studies consistently show that a significant percentage of website images are missing alt text entirely, leaving rankings and accessibility improvements on the table.
This complete guide covers everything you need to know about image alt text for SEO: what it is, why it matters, how to write it effectively, and how to audit your existing images to find and fix missing or poorly written alt attributes.
What Is Image Alt Text
Image alt text, short for alternative text, is an HTML attribute added to the <img> tag that provides a text description of the image. In HTML, it looks like this:
<img src="seo-dashboard.png" alt="SEO audit dashboard showing page speed scores and heading analysis">
The alt attribute serves three distinct functions. First, it provides a text alternative for screen reader users who cannot see the image, making your content accessible to people with visual impairments. Second, it displays as placeholder text when an image fails to load due to a broken URL, slow connection, or browser settings that block images. Third, it provides search engines with contextual information about the image, enabling them to index and rank it in image search results.
Alt Text vs. Title Text vs. Caption
Alt text is sometimes confused with image title attributes and visible captions, but these serve different purposes. The alt attribute is the primary text alternative for the image and is essential for accessibility and SEO. The title attribute creates a tooltip that appears when users hover over the image, but it is not announced by most screen readers and has minimal SEO value. Image captions are visible text below the image that provides additional context; they are helpful for users but do not replace the need for alt text. For optimal results, use alt text on every informational image and add captions when additional explanation benefits the reader.
The Alt Attribute in HTML
The alt attribute is a required attribute on all <img> elements according to HTML specifications. Omitting it entirely is different from using an empty alt attribute. An empty alt attribute (alt="") tells screen readers to skip the image, which is appropriate for decorative images. Omitting the alt attribute entirely causes screen readers to announce the image file name, which creates a poor user experience. Always include the alt attribute, even if the value is an empty string for decorative images.
Why Alt Text Matters for SEO
Image alt text plays a more significant role in SEO than many website owners realize. It impacts your visibility across multiple search channels and contributes to your overall page relevance.
Google Image Search Traffic
According to Google's best practices for Google Images, alt text is one of the primary factors Google uses to understand what an image depicts. Well-optimized alt text helps your images appear in Google Image Search results, which can drive significant additional traffic to your site. Image search is particularly valuable for visual industries like e-commerce, travel, food, and design, where users frequently begin their search journey through images.
Page-Level Relevance Signals
Alt text contributes to the overall topical relevance of your page. When your images have alt text containing relevant keywords, it reinforces the page's theme for search engines. This is especially important when images support the surrounding text content. For example, a page about SEO audits with images showing audit reports and dashboard screenshots, each described with relevant alt text, sends stronger topical signals than the same page with generic or missing alt text.
Accessibility and Compliance
Web accessibility is not just a moral obligation; it is increasingly a legal requirement. Many jurisdictions require websites to comply with accessibility standards such as WCAG 2.1, which mandates text alternatives for non-text content. Missing alt text is one of the most common WCAG violations. Ensuring all your images have appropriate alt text protects your organization from accessibility-related legal issues while serving a broader audience. Search engines also favor accessible websites, as Google has indicated that accessibility improvements can indirectly benefit SEO performance.
How to Write Effective Alt Text
Writing good alt text is a skill that balances descriptiveness with conciseness. Follow these principles to create alt text that serves both users and search engines effectively.
Be Specific and Descriptive
Describe what the image actually shows, not what you think it represents metaphorically. If the image shows a bar chart comparing organic traffic across three months, say that. If it shows a person typing on a laptop, describe the specific scene. Vague descriptions like "chart" or "person" miss the opportunity to convey meaningful information. Aim for enough detail that someone who cannot see the image can understand what it depicts and why it is relevant to the surrounding content.
Keep It Concise
While specificity is important, alt text should not be a paragraph. Aim for 5 to 15 words that capture the essential content of the image. Screen readers announce alt text in a continuous flow, so overly long descriptions become tedious for users to listen to. If an image requires extensive description, such as a complex infographic, consider providing the detailed description in the surrounding page content and using a shorter summary as the alt text.
Include Keywords Naturally
When relevant, include your target keyword or a semantic variation in the alt text. This should happen naturally, not as a forced insertion. If your page is about content optimization for SEO and the image shows an optimization checklist, alt text like "SEO content optimization checklist with 10 on-page factors" naturally incorporates the keyword while accurately describing the image. Never add keywords to alt text when they do not relate to what the image actually shows.
Describe Function for Interactive Images
When images function as links or buttons, the alt text should describe the action or destination, not the image itself. For a search icon that triggers a search function, the alt text should be "Search" rather than "magnifying glass icon." For a logo that links to the homepage, "Company Name - Home" is more useful than "company logo." The alt text for functional images should tell users what will happen when they interact with the element.
Alt Text Examples: Good vs. Bad
Seeing concrete examples makes it easier to understand the difference between effective and ineffective alt text. Here are comparisons across several common scenarios.
Product Images
Bad: alt="shoe" -- This is too vague and provides no useful information about the specific product.
Bad: alt="best running shoe buy now cheap running shoe for marathon training exercise fitness" -- This is keyword-stuffed spam that helps neither users nor search engines.
Good: alt="Navy blue running shoe with white mesh upper and cushioned sole, side view" -- This describes the specific product with relevant details that help both accessibility and search visibility.
Charts and Data Visualizations
Bad: alt="chart" -- This tells the user nothing about what data the chart presents.
Good: alt="Bar chart showing 45% increase in organic traffic from January to March 2026" -- This communicates the key takeaway from the data visualization.
Team and People Photos
Bad: alt="IMG_4582.jpg" -- This is the file name being used as alt text, likely because no alt attribute was provided and the CMS defaulted to the file name.
Good: alt="Marketing team collaborating on SEO strategy around a conference table" -- This describes the scene and provides context for why the image appears on the page.
Screenshots and Interface Images
Bad: alt="screenshot" -- Completely unhelpful for understanding what the screenshot shows.
Good: alt="Elvisto dashboard showing heading hierarchy analysis with three warnings flagged" -- This describes the specific interface elements visible in the screenshot, giving context to the surrounding content.
Alt Text for Different Image Types
Different types of images require different approaches to alt text. Understanding these distinctions ensures you apply the right strategy to each image on your site.
Informational Images
Images that convey information essential to understanding the page content need descriptive alt text that captures their meaning. These include product photos, diagrams, charts, screenshots, and photos that illustrate points made in the text. The alt text should describe what the image shows in enough detail that a user who cannot see it can still understand the content fully.
Decorative Images
Images that serve a purely aesthetic purpose, such as background patterns, visual dividers, or generic stock photos used for visual appeal, should have an empty alt attribute (alt=""). This prevents screen readers from announcing irrelevant descriptions and keeps the listening experience clean and focused. Identifying which images are truly decorative requires judgment; if removing the image would reduce the page's informational value, it is not decorative.
Complex Images
Infographics, detailed diagrams, and complex charts may contain more information than can be conveyed in a concise alt text. For these images, provide a brief summary in the alt attribute and include a full text description in the surrounding page content. This approach satisfies both accessibility requirements and SEO needs, as the detailed description adds keyword-rich content to the page while the alt text provides the screen reader summary. Your heading structure can help organize these longer descriptions within your page content.
Linked Images
When an image serves as a link, the alt text should describe the link destination or action rather than the image appearance. For a thumbnail that links to a full article, the alt text should indicate the article topic. For an icon that initiates a download, the alt text should describe what will be downloaded. If the linked image already has adjacent link text describing the destination, the image alt text can be empty to avoid redundancy.
Common Alt Text Mistakes
Avoiding these frequent mistakes will immediately improve your image optimization and accessibility compliance.
Starting with "Image of" or "Photo of"
Screen readers already announce that an element is an image before reading the alt text, so prefixing your alt text with "Image of" or "Photo of" creates redundancy. Instead of "Image of a sunset over the ocean," simply write "Sunset over the ocean with orange and purple sky." The exception is when the medium matters, such as "Oil painting of a sunset" where the fact that it is a painting is relevant information.
Using File Names as Alt Text
Alt text like "DSC_0042.jpg" or "hero-banner-v2-final.png" provides zero value to users or search engines. This typically happens when alt attributes are left empty and the CMS defaults to the file name, or when content editors paste the file name into the alt field. Audit your site to find these instances and replace them with meaningful descriptions.
Keyword Stuffing
Cramming multiple keywords into alt text is a spammy practice that degrades accessibility and can trigger search engine penalties. Alt text like "SEO audit tool SEO checker website SEO analysis free SEO" is harmful to your site's reputation with both users and search engines. Use one relevant keyword naturally within a descriptive phrase, and only when it genuinely relates to the image content.
Leaving Alt Text Empty on Informational Images
Every image that conveys information needs alt text. Leaving the alt attribute empty (or omitting it) on product images, diagrams, screenshots, or other content-relevant images creates accessibility barriers and misses SEO opportunities. If you have a large site with thousands of images, prioritize adding alt text to images on your highest-traffic pages first, then work through the rest systematically. A technical SEO checklist can help you track this progress.
Auditing Your Site's Alt Text
Regular alt text audits ensure your site maintains both SEO performance and accessibility standards as new content is added.
What to Check in an Alt Text Audit
A thorough alt text audit should identify images with missing alt attributes, images with empty alt on informational content, images with file names used as alt text, images with keyword-stuffed alt text, decorative images that have non-empty alt text, and images with alt text that does not match the image content. Each of these issues represents either an SEO opportunity or an accessibility barrier that should be addressed.
Automated Scanning Tools
Manually checking every image on a large website is impractical. SEO auditing tools like Elvisto scan your pages automatically and flag images with missing, empty, or potentially problematic alt text. These tools provide a prioritized list of issues, making it easier to focus your optimization efforts where they will have the greatest impact. Automated scanning also catches issues that might be missed during manual review, such as images added through CMS widgets or dynamic content.
Creating Alt Text Guidelines for Your Team
If multiple people add content to your website, establish clear alt text guidelines that everyone follows. Document your standards for different image types, provide examples of good and bad alt text, and include alt text review as part of your content publishing workflow. Consistency across your site improves both accessibility and SEO performance. Training your content team on broader content optimization practices ensures alt text is part of a comprehensive quality standard.
Frequently Asked Questions
What is image alt text?
Image alt text (alternative text) is an HTML attribute added to image tags that provides a text description of the image. It serves three purposes: it describes the image for screen reader users who cannot see it, it displays as placeholder text when an image fails to load, and it helps search engines understand what the image depicts for image search rankings.
How long should alt text be?
Alt text should generally be between 5 and 15 words, or roughly 125 characters or fewer. It should be descriptive enough to convey the image's content and context but concise enough that screen readers can announce it quickly. Avoid writing alt text that exceeds a full sentence unless the image contains complex information like a chart or infographic.
Should decorative images have alt text?
Decorative images that do not convey meaningful content should have an empty alt attribute (alt=""). This tells screen readers to skip the image entirely, preventing unnecessary announcements. Examples of decorative images include visual spacers, background patterns, and ornamental dividers. Never omit the alt attribute entirely, as this causes screen readers to announce the file name instead.
Does alt text help with Google Image Search rankings?
Yes, alt text is one of the primary factors Google uses to understand and rank images in Google Image Search results. Well-written alt text that accurately describes the image content and includes relevant keywords helps your images appear in image search results, driving additional traffic to your site. Google has specifically stated that alt text is important for image search optimization.
Every informational image on your site needs descriptive alt text that accurately describes the image content in 5-15 words. Include relevant keywords naturally, use empty alt attributes for decorative images, and avoid keyword stuffing or generic descriptions. Regular alt text audits catch missing and problematic alt attributes before they impact your SEO performance or accessibility compliance.