Images play a critical role in digital content, helping to convey information, engage users, and enhance storytelling. But for people who are blind or visually impaired, images alone don’t provide value unless they are accompanied by descriptive and meaningful alternative text (alt text).

When it comes to simple images—like icons, buttons, or decorative visuals—writing alt text is straightforward. But what about complex images like charts, infographics, maps, and diagrams? These images often carry dense information, and writing effective alt text requires more thought and strategy.

In this post, we’ll break down the best practices for writing clear, concise, and useful alt text for complex images, ensuring that your content is accessible to everyone.

Why Alt Text Matters for Accessibility

Alt text is essential for users who rely on screen readers, which convert text into speech or braille. Without alt text, screen reader users miss out on critical information that sighted users can perceive visually.

Providing accurate and meaningful alt text is required under Web Content Accessibility Guidelines (WCAG) and laws like the Americans with Disabilities Act (ADA) and Section 508. But beyond compliance, well-crafted alt text improves user experience, search engine optimization (SEO), and content comprehension for a wide audience.

Types of Complex Images & How to Write Alt Text for Them

1. Charts and Graphs

Challenge: Charts present data visually, often comparing values or showing trends. Simply saying “Bar chart showing sales data” isn’t useful. The goal is to summarize the key takeaways.

Best Practices:

• Focus on the main insight the chart conveys.
• If needed, provide detailed descriptions elsewhere (e.g., in a data table or a caption).
• Keep the alt text concise but meaningful.

Example:
Image: A bar chart showing annual revenue growth.
Bad Alt Text: “Bar chart of company revenue.”
Good Alt Text: “Bar chart showing company revenue growing from $5M in 2021 to $12M in 2023, with a 140% increase over three years.”

Pro Tip: If a chart has complex data, provide a text alternative directly below the image or in a separate linked document.

2. Infographics

Challenge: Infographics contain text, icons, and multiple data points, making them harder to describe in a single alt text entry.

Best Practices:

• Provide a brief summary in the alt text.
• Offer a longer, detailed description in a nearby text block or linked page.

Example:
Image: An infographic explaining “5 Tips for Remote Work Productivity.”
Bad Alt Text: “Infographic about remote work.”
Good Alt Text: “Infographic titled ‘5 Tips for Remote Work Productivity,’ listing strategies such as setting a schedule, using collaboration tools, and taking regular breaks. Full details provided below.”

Pro Tip: If an infographic contains text-heavy content, don’t repeat every word in the alt text—instead, provide a text version of the content on the same page.

3. Maps

Challenge: Maps often convey geographic locations, routes, or data distribution that sighted users can understand at a glance. Screen reader users need descriptive context.

Best Practices:

• Identify the purpose of the map (Is it showing locations? A route? A population trend?).
• Describe key landmarks or trends, not every detail.
• If necessary, offer a link to a text-based version with more specifics.

Example:
Image: A map showing the locations of company offices in different states.
Bad Alt Text: “Map of the United States with office locations.”
Good Alt Text: “Map of the United States with company offices marked in New York, Chicago, and Los Angeles. A full list of addresses is available below.”

Pro Tip: If the map is interactive, ensure keyboard accessibility and provide alternative navigation options.

4. Diagrams & Flowcharts

Challenge: Diagrams and flowcharts illustrate processes, relationships, and hierarchies, which can be hard to convey in a short description.

Best Practices:

• Summarize the overall process or relationship in the alt text.
• If needed, provide a step-by-step explanation below the image.

Example:
Image: A flowchart showing the customer onboarding process.
Bad Alt Text: “Flowchart showing customer onboarding.”
Good Alt Text: “Flowchart illustrating the four-step customer onboarding process: 1. Sign-up, 2. Verification, 3. Setup, and 4. First Purchase. Full details below.”

Pro Tip: If a diagram is highly detailed, consider linking to a text-based version or providing an HTML alternative.

General Tips for Writing Effective Alt Text for Complex Images

1. Keep it concise but meaningful.

• Alt text should be short but still informative.
• Avoid unnecessary words like “Image of” or “Picture of” (screen readers already announce it’s an image).

2. Focus on the key message.

• What is the most important takeaway from the image?
• If a sighted user asked, “What does this image show?”—how would you summarize it?

3. Use captions & surrounding text wisely.

• If an image needs a long description, provide a caption or text-based alternative nearby.
• Don’t repeat alt text and captions verbatim—use them to complement each other.

4. Provide alternative formats when needed.

• If a complex image contains too much detail, offer a text-based version, a linked document, or an audio description.

5. Test with a screen reader.

• Use tools like NVDA (Windows), VoiceOver (Mac/iOS), or JAWS to check how alt text is read aloud.
• Ask real users (especially those who rely on screen readers) for feedback.

Final Thoughts: Accessibility Benefits Everyone

Writing alt text for complex images may take extra effort, but it ensures that everyone—regardless of ability—can access and understand your content.

By following best practices, you:
Improve accessibility for users with visual impairments
Enhance SEO and discoverability
Provide a better user experience for all

Let’s make the web a more inclusive place—one image at a time.