Creating Image Descriptions

Creating Image Descriptions

Effective image descriptions are essential for making content accessible to all learners. Good image description practices include deciding when to use concise alt text, when to mark an image as decorative, and when a more detailed explanation is needed for a complex visual. While some images can be described in a few words, others—such as charts, graphs, maps, and diagrams—require more explanation to communicate their instructional purpose. This chapter explains how to choose the right type of image description, how alt text and long descriptions work together, and how AI tools can support the drafting process while still requiring human review.

Chapter Overview

This chapter explains how to create accessible image descriptions for a range of visual content. It introduces the purpose of alt text, when to treat an image as decorative, when to write a long description, and how to describe visuals in ways that support learning. It also highlights examples of complex images and emphasizes formatting practices that improve readability and accessibility.

Why Image Descriptions Matter

Image descriptions help ensure that learners can access visual information regardless of how they interact with digital content. A student using a screen reader depends on text alternatives to understand what an image contributes to the page. Image descriptions can also help learners who have low bandwidth, who disable images, or who benefit from text-based explanations of visual material.

In educational content, an image description should focus on the image’s instructional purpose. Instead of describing every visible detail, describe what the learner needs to know to understand the concept, process, relationship, or data being presented.

Types of Image Descriptions

Not every image needs the same kind of description. Choosing the correct approach improves both accessibility and clarity.

• Informative images need concise alt text that communicates the key idea.
• Decorative images should use empty alt text so assistive technologies skip them.
• Functional images should be described by what they do, such as “Search” or “Download syllabus.”
• Complex images usually need both short alt text and a longer description.

For example, a photo used only to add visual interest may not need a spoken description, while a diagram of the water cycle or a chart showing enrollment trends may require more explanation.

Purpose of Alternative Text

Alternative text, also known as alt text, is descriptive text that conveys the meaning or function of an image in digital content. It is designed to make visual content accessible to people with vision disabilities.

When a person uses assistive technology such as a screen reader, the screen reader will read the onscreen text aloud. When the screen reader reaches an image, it will read the alt text for that image so the user can know what the image is meant to convey. Images can provide illustrative information, or they can act as buttons and similar interactive elements, so the alt text must describe these aspects to the user so they can respond appropriately.

Without alt text, people who use screen readers cannot access the content provided in the images. This is why alt text is a requirement in Section 508 guidance for creating digital content.

Additionally, alt text makes content accessible to other users, such as those who may have difficulty interpreting visual content or users without access to high-speed internet who cannot load images on the web. It also makes visual content available for technical applications such as search, digital assistants, and artificial intelligence tools.

Alt text can be created simply by using some advanced AI tools. Tools like the Image Accessibility Generator from Arizona State University can make this process much easier.

Writing Effective Alt Text

Effective alt text is brief, purposeful, and connected to the learning context. A useful description usually answers one question: what does this image need to communicate here?

Keep these practices in mind:

• Be concise.
• Focus on the meaning or function of the image.
• Avoid beginning with phrases such as “image of” or “picture of” unless that distinction matters.
• Match the description to the surrounding content and learning goal.
• Do not repeat nearby text unless repetition is necessary for clarity.

For example, if a chapter discusses a bar chart comparing graduation rates, the alt text should identify the chart and its topic rather than simply saying “bar chart.”

Decorative and Functional Images

Some images do not need a descriptive alt text, while others need a function-focused one.

A decorative image does not add instructional meaning. For example, a patterned divider, background flourish, or stock image used only for visual appeal should use empty alt text (alt="") so screen readers skip it.

A functional image does something. If an image is used as a button, link, or icon, the description should explain the action. For example:

• Functional alt text: Submit assignment
• Functional alt text: Open chapter menu

This helps users understand what will happen when they activate the image.

When to Use a Long Description

Use a long description when an image contains important details that cannot be communicated clearly in a short alt text field. Long descriptions are especially useful when the surrounding text depends on readers understanding the visual.

Common examples include:

• Charts and graphs
• Flowcharts and organizational charts
• Diagrams and detailed illustrations
• Maps showing locations or patterns such as weather systems
• Timelines with multiple events or relationships

How Alt Text and Long Descriptions Work Together

Images that have a long description still need alt text. The alt text should be short and should connect the image to the longer explanation.

For example, the alt text might identify the image and point the reader to the longer description:

• Alt text: Chart of enrollment trends, long description below.
• Long description: The chart shows that enrollment increased steadily from 2020 to 2024, with the largest rise occurring between 2022 and 2023.

This approach gives readers a quick identifier in the alt text and then provides the full explanation in a more suitable location.

Example

A simple example might look like this:

• Alt text: Graph A, long description below.
• Long description: Graph A shows that…

Formatting Long Descriptions

Long descriptions should be formatted like other accessible content. Use headings, paragraphs, and lists when appropriate so the description is easy to read and navigate.

For charts and graphs, include a data table alongside the visual whenever possible. A table often provides a strong alternative way to present the same information.

A strong long description often includes:

• The type of image
• The topic or purpose of the visual
• The most important relationships, trends, or labels
• Any conclusions or patterns the learner needs to notice

Where to Place a Long Description

Because a long description is too detailed for an alt text field, place it in one of these locations:

• In the surrounding page text, near the image
• In a linked document, such as a Word file, when space is limited

Describing the image in the surrounding text is often the best option because it benefits all readers, not only those using assistive technology.

Using AI to Generate Image Descriptions

AI tools like the ASU Image Accessibility Creator allow users to upload images and automatically generate alt text and detailed descriptions, helping streamline the creation of accessible content. While these tools provide a strong starting point, the output should always be reviewed and refined to ensure accuracy, clarity, and alignment with the learning context.

AI can be especially useful for:

• Generating a first draft of alt text
• Identifying visible elements in a complex image
• Drafting a longer explanation for charts, maps, and diagrams
• Helping revise descriptions for clarity and readability

AI can significantly support accessibility efforts, but human judgment remains essential to produce meaningful and effective image descriptions.

Reviewing Image Descriptions for Accessibility

After writing image descriptions, review them as part of your normal accessibility check.

Ask:

• Does the description match the image’s instructional purpose?
• Is the alt text concise and meaningful?
• Is the image decorative and better skipped with empty alt text?
• Does a complex image include a long description or alternative format such as a table?
• Can a learner understand the visual content without seeing the image?

This review process helps ensure that image descriptions support both accessibility and comprehension.