How Alt Text Impacts SEO: The Intersection of Accessibility and Search Rankings

In our previous articles, we explored how to identify which images require alt text and best practices for writing effective alt text from an accessibility perspective. Now, we’ll examine how properly implemented alt text can also significantly boost your search engine performance.

While accessibility should be your primary motivation for implementing alt text, the SEO benefits provide an additional compelling reason to invest in this practice. This article explores the mechanisms behind alt text’s impact on search rankings and how to optimize your approach without compromising accessibility.

How Search Engines Use Alt Text

Search engines rely on alt text for several critical functions:

1. Image Indexing and Understanding

Unlike humans, search engine crawlers cannot “see” images. Alt text serves as the primary mechanism for these crawlers to understand:

• What the image depicts
• How it relates to surrounding content
• Which search queries it might be relevant for

Google’s image recognition technology has advanced significantly, but it still relies heavily on textual cues like alt text to confirm image content and context.

2. Keyword Relevance Signals

Alt text provides search engines with additional context about your page’s topic and focus:

• Each properly described image reinforces your page’s topical relevance
• Thematically consistent alt text helps search engines understand your content’s focus
• Images with relevant alt text can rank in both standard and image search results

3. User Experience Indicators

Search engines increasingly factor user experience into rankings:

• Accessible sites with proper alt text tend to have lower bounce rates
• Better engagement metrics signal quality content to search algorithms
• Accessible images contribute to Core Web Vitals scores, particularly Largest Contentful Paint (LCP)

Potential Impact: How Alt Text Could Improve Search Performance

While specific results will vary by organization, industry research suggests that optimizing alt text can significantly impact search visibility. Here is a realistic scenario showing how organizations might benefit:

Water Utility Infrastructure Pages

Scenario: A municipal water utility implementing descriptive alt text for infrastructure images.

Implementation Example:

• Before: <img src="treatment-facility.jpg" alt="water treatment plant">
• After: <img src="treatment-facility.jpg" alt="Mountain Water Treatment Facility using reverse osmosis filtration system serving 50,000 residents.">

Potential Benefits:

• Improved visibility for searches related to specific treatment technologies
• Better ranking for local water quality information queries
• Enhanced find-ability of infrastructure and service information

Balancing SEO Keywords and Accessibility Needs

The art of optimizing alt text lies in balancing search visibility with accessibility requirements:

1. Prioritize Accuracy and Clarity

Always prioritize accurate descriptions over keyword placement:

• Ensure the alt text accurately reflects the image content
• Focus on clarity for screen reader users first
• Add relevant keywords only when they enhance understanding

2. Strategic Keyword Integration

When including keywords in alt text:

• Place primary keywords near the beginning when natural
• Use synonyms and related terms rather than exact keyword repetition
• Maintain natural language patterns that screen readers can interpret properly

3. Context-Aware Optimization

Optimize alt text based on each image’s specific purpose:

• For infrastructure images: Include facility name, technology used, and population served
• For process diagrams: Describe key stages and outcomes with relevant technical terminology
• For public service images: Include program names and citizen benefits
• For informational images: Describe the information being conveyed with relevant terminology
• For decorative images: Maintain empty alt text (alt="") regardless of SEO opportunities

4. Avoid Over-Optimization

Signs your alt text is over-optimized:

• Keyword stuffing (e.g., alt="best SEO consultant SEO services affordable SEO expert")
• Irrelevant keywords not represented in the image
• Unnatural phrasing focused on search terms rather than description
• Identical alt text across multiple images

Common Mistakes That Hurt Both SEO and Accessibility

Many practices can undermine both your accessibility compliance and search performance:

1. Missing Alt Text

Images without alt attributes:

• Are inaccessible to screen reader users
• Provide no content for search engines to index
• Represent missed opportunities for keyword relevance
• May trigger accessibility validation warnings

It’s important to note that this refers to meaningful images that require description. As we explained in our article on distinguishing between meaningful and decorative images, truly decorative images should have empty alt text (alt="") rather than missing the alt attribute entirely. This empty alt text properly indicates to assistive technologies that the image can be skipped, while still maintaining valid HTML and passing accessibility validators.

2. Generic Descriptions

Vague alt text like “image” or “photo”:

• Provides no meaningful information to screen reader users
• Offers no SEO value for search engines
• Wastes opportunities to reinforce page relevance
• May trigger accessibility validation warnings

3. Filename as Alt Text

Using image filenames as alt text:

• Creates poor screen reader experiences (e.g., “product_image_0043.jpg”)
• Provides limited or confusing context for search engines
• Often contains underscores or hyphens that screen readers may pronounce
• May trigger accessibility validation warnings

4. Excessive Length

Alt text that’s too long:

• May be truncated by some screen readers
• Dilutes the focus of your description
• Often indicates content that should be placed elsewhere, such as:
  • In a figcaption element
  • In the surrounding main text
  • In an ARIA-describedby linked description
  • Using a more detailed adjacent description

As we covered in our article on writing effective alt text, there are several structured ways to provide detailed image descriptions without overloading the alt attribute.

5. Inconsistent Implementation

Inconsistent alt text patterns across your site:

• Create unpredictable experiences for assistive technology users
• Confuse search engines about image relationships and hierarchies
• Result in missed optimization opportunities

Auditing Your Alt Text for SEO Impact

Regular audits help ensure your alt text serves both accessibility and SEO purposes:

1. Automated Scanning Tools

Use a combination of accessibility and SEO tools:

• Accessibility scanners: WAVE, axe, or Lighthouse to identify missing alt text
• SEO crawlers: Screaming Frog, Semrush, or Ahrefs to analyze alt text patterns
• Google Search Console: Review image search performance and indexing issues

2. Manual Image Sampling

Regularly review a sample of images across your site:

• Check if alt text accurately describes each image
• Evaluate whether key terms are included when appropriate
• Ensure consistency in how similar images are described

3. Analytics Integration

Track image performance in your analytics:

• Monitor traffic from image search
• Compare engagement metrics for pages with optimized vs. unoptimized images
• Track conversion rates from image search traffic

4. Competitor Analysis

Benchmark your implementation against industry leaders:

• Review alt text on top-ranking competitor pages
• Identify patterns in how they describe similar images
• Look for gaps in their implementation you can leverage

Implementation Strategy: The Alt Text Optimization Process

Follow this process to systematically improve both accessibility and SEO:

1. Inventory your images: Categorize images by type (product, informational, decorative, etc.)
2. Prioritize optimization: Focus first on high-value pages and critical images
3. Create templates: Develop consistent patterns for similar image types:

This guide provides general information and should not be construed as legal advice. Organizations should consult with qualified legal professionals for specific guidance on compliance requirements.