What Is Alt Text and Why Does It Matter for Accessibility?

Images are a key part of today’s digital landscape. From websites to social media, they help convey information, tell stories, and engage audiences.

But images don’t work the same way for everyone. How do people who are blind or have low vision understand visual content? How do they navigate image-heavy digital experiences?

That’s where alt text comes in.

What is Alt Text?

Alt text — also called alternative text — is a written description of an image that screen readers can read out loud (or convert to Braille) so people with visual impairments, sensory processing disorders, or learning disorders can understand their content and purpose. Image alt text is also displayed if an image fails to load, helping search engine bots understand the contents of the image.

What Does Alt Text Do?

Alt text is typically added to your HTML code using the “alt” attribute on an image element. At a code level, it may look like this:

<img src="image.jpg" alt="Description of the image">

But what actually happens behind the scenes is where alt text accessibility really matters.

When a screen reader encounters an image, it checks for alt text. If it’s present, the screen reader announces that text aloud to the user. If it’s missing, the experience can quickly fall apart — some screen readers will announce the file name, while others will simply say “image,” leaving the user with zero context.

Here’s a more practical example:

Brown and white dog standing in tall grass and surrounded by white flowers.

Strong alt text for this image might be: “Brown and white dog standing in tall grass surrounded by white flowers.”

When a screen reader encounters this image, it will read the description as part of the page content, allowing someone who is visually impaired to understand what’s being communicated visually. 

Alt Text vs. Image Description

A quick note: Alt text is not the same as an image description. Alt text is typically invisible to sighted users, whereas image descriptions (also known as captions) are displayed directly in the web browser. Captions can also include additional details about an image, such as photo credits or copyright information.

Why is Alt Text Important for Accessibility?

Alt text plays a critical role in making digital content usable for people with disabilities, particularly assistive technology users. 

For people who use screen readers, alt text is what turns an image into meaningful information. When an image includes a clear, accurate description, a screen reader announces it as part of the page content, allowing the user to understand what’s being portrayed visually. Without alt text accessibility, that same user may hear a generic file name or nothing at all, which can break context and make the experience confusing or incomplete.

Alt text also supports people with cognitive disabilities, attention-related challenges, or sensory sensitivities. Pages that rely heavily on images can feel overwhelming, and some users choose to disable images entirely to improve focus or reduce cognitive load. When alt text is present, the content remains understandable — even when visuals are turned off — ensuring no information is lost.

Beyond usability, alt text is a foundational requirement for digital accessibility compliance. Accessibility laws such as the Americans with Disabilities Act(opens in a new tab) (ADA), the European Accessibility Act(opens in a new tab) (EAA), and the Accessibility for Ontarians with Disabilities Act(opens in a new tab) (AODA) rely on the Web Content Accessibility Guidelines(opens in a new tab) (WCAG) to define accessibility standards.

WCAG Success Criterion 1.1.1(opens in a new tab) requires that non-text content, including images, have text alternatives so that people with disabilities can perceive and interact with the content.

When images lack alt text, websites fail to meet this core WCAG requirement, which can put organizations at risk of noncompliance with accessibility laws, such as the ADA, and potentially expose them to demand letters or lawsuits.

While alt text may also support search engines in understanding page content, its primary purpose is accessibility. At its core, alt text accessibility ensures everyone — regardless of ability — has equal access to the information on your website.

Examples of Good vs. Poor Alt Text

The easiest way to understand effective alt text is to see how small wording changes can completely change the meaning of an image. The alternative text examples below show how context determines whether alt text actually helps someone understand the content.

Example 1: Business Meeting Image

The image shows men and women in a conference room discussing a financial chart displayed on a whiteboard.

Poor alt text:

“Group of people attending a meeting”

This decision identifies the presence of people but misses the point of the image. Someone using a screen reader knows a meeting is happening, but not why the image matters. 

Better alt text:

“Men and women in a conference room talking.”

This adds visual detail, but still lacks context. It doesn’t explain what’s being discussed or how the image supports the surrounding content.

Good alt text:

“A group of professionals in a conference room reviewing a financial chart on a whiteboard.”

This version communicates meaning. It tells the user what’s happening and why the image exists, which is the goal of accessible alt text images.

Example 2: Puppy Image on a Veterinary Website

Poor alt text:

“Golden retriever puppies.”

This description is technically accurate, but incomplete. It doesn’t reflect the purpose of the image within the page.

Better alt text:

“Golden retriever puppies at a vet.”

More context, but still vague.

Good alt text:

“Golden retriever puppies receiving their first vaccinations at a veterinary clinic.”

Here, the alt text supports the page’s message, rather than just describing what’s visible. This is a strong example of how alt text should show context, not just content.

What These Examples Have in Common

Across both alternative text examples, effective alt text follows the same core principles:

• It explains the purpose of the image, not just the objects in it.

• It avoids filler phrases like “picture of” or “image of”.

• It presents the most important information first.

• It’s written for people first — not search engines.

Why This Matters

When alt text lacks context, people using assistive technology are forced to guess. When it’s done well, they receive the same information and intent as someone viewing the image visually.

That’s the difference between technically present alt text and meaningful alt text.

Icons representing five types of images: Informative, Decorative, Functional, Text, and Complex.

When is Alt Text Required?

According to WCAG guidelines, all images must have a text alternative that describes their function or the information they represent. However, that doesn’t mean every image should be treated the same. 

Below is an overview of different image types and how to write image alt text for each one:

• Informative images: If a picture, photo, or illustration is intended to visually represent an important concept or piece of information, the image alt text should provide a concise description that conveys the essential information presented by the image.

• Decorative images: If an image’s only purpose is to add visual decoration (rather than convey information that’s important to understanding the page), adding a null (empty) text alternative (alt=””) tells assistive technologies not to announce the image. WCAG recommends using alt text for all decorative images to ensure a seamless experience.

• Functional images: If an image is used as a link or button (such as a printer icon to represent the print function), the alt text should describe the functionality of the link or button, rather than the image itself.

• Image of text: If readable text is presented within an image, the text alternative should contain the same words as the image.

• Complex images: To convey data or detailed information (such as a graph or diagram), alt text should be a complete text equivalent of the information presented in the image.

Not sure how to treat a specific image? The W3C has developed an alt text decision tree(opens in a new tab) to help you choose the right alt text based on the image’s purpose.

Common Alt Text Mistakes to Avoid

Even with the best intentions, alt text images often fall short in predictable ways. Understanding these common mistakes can help ensure your alt text actually improves accessibility — rather than creating new barriers. 

Keyword Stuffing

Trying to force keywords into alt text can make descriptions awkward and difficult for screen reader users to follow. Alt text should describe the meaning and context first. If a keyword fits naturally into that description, that’s fine — but it should never come at the expense of clarity.

Redundant Descriptions

Repeating information that’s already provided in nearby text or captions adds unnecessary noise for assistive technology users. Alt text should supplement content, not duplicate it.

Missing Context

Describing what an image looks like without explaining why it matters is one of the most common alt text mistakes. Effective alt text images communicate purpose, not just objects.

Treating All Images the Same

As mentioned above, not every image needs descriptive alt text. Decorative images should be skipped using a null alt attribute so they don’t interrupt the user experience. Failing to recognize this distinction can overwhelm screen reader users with unnecessary content.

Over-Describing Images

Alt text isn’t a narration. Including excessive detail can bury the point of the image and make pages harder to navigate. Focus on what’s essential to understanding the content.

Take the Next Steps Towards Accessibility

Alt text is essential for helping people with visual or cognitive disabilities interact with and understand your digital content. Descriptive alt text gives context to images, ensuring readers don’t miss key information and can fully engage with your page.

Even the best intentions can leave gaps, though — missing or unclear alt text can slip through unnoticed, making parts of your site inaccessible to users who rely on assistive technology. That’s where AudioEye comes in.

AudioEye’s Website Accessibility Checker identifies missing alt text and other common accessibility issues, giving you a clear, actionable starting point for improving your site. For more complex cases, our team of accessibility experts and human testers evaluates content, such as non-descriptive alt text, to help you prioritize fixes efficiently. The result? A more accessible website and a smoother experience for all.

Scan your website below to see how accessible your content really is and uncover opportunities to make your site more accessible and compliant.