Alternative Text for Images

Alternative text (alt text) provides a meaningful alternative to visual content such as images, charts and graphs. It ensures that individuals who have difficulty perceiving visual information—such as people who are blind or have low vision—can still access the content of an image and understand its purpose.

To be effective, alternative text should briefly describe the image in a way that conveys its content and the reason it was included.

Impact

Alt text plays a vital role in making digital content accessible. Assistive technologies like screen readers use alt text to describe images to users who are blind, have low vision or otherwise cannot perceive visual content. Without it, an image is essentially invisible—present but without meaning—much like a broken image icon to a sighted user.

This lack of context can be critical. If an image conveys important information, omitting alt text can prevent someone from fully understanding the content or completing a task.

Alt text also benefits sighted users. When images fail to load due to slow connections or are disabled in email clients, alt text is displayed in place of the image. Without it, users are left with only a blank space or broken icon, missing potentially valuable information.

How to provide effective alternative text

Writing effective alternative text (alt text) is essential for ensuring that visual content is accessible to all users. While alt text should be concise, it must also convey the purpose and meaning of the image within its context.

Key principles

• Be concise but meaningful: Describe what the image shows and why it matters in the context of the content. Aim for one or two sentences.
• Focus on function, not form: Don’t describe every visual detail—only include what’s necessary to understand the image’s purpose. Consider how you would describe the key points of the image to someone on the telephone.
• Avoid redundancy: Don’t repeat information that’s already conveyed in nearby text or captions.
• Use plain language: Write clearly and simply so that the description is easy to understand when read aloud by a screen reader.

Informative vs. decorative images

Informative images convey essential information. These include charts, graphs, diagrams and photos that support or enhance the content. These images must have descriptive alt text that communicates their purpose.

Example:

Alt text for the image: “Six people gather around the Rehabilitation Education Center sign outside of DRES.”

Decorative images are used purely for visual appeal and do not add meaningful content. These images should be marked as decorative so that screen readers skip them and users are not distracted by irrelevant information. This can be done in word processing programs or in a CMS by checking the appropriate box in the interface to add alt text or by using empty alt text (i.e., alt="") in HTML.

Example:

The above is an image of Foellinger Auditorium, commonly used for website banners on campus. It does not provide meaningful content when used as a background image and would be considered decorative.

When alt text isn’t enough: Complex images

Some images—such as detailed charts, graphs and infographics—contain too much information to be fully described in a short alt text. In these cases:

• Use concise alt text to summarize the image.
• Provide full in-text description to describe relevant details of the image. For charts or graphs, it may be appropriate to provide an accompanying table of the data.

Example:

(Image Credit: WebAIM)

Alt text for the image: "Pie chart showing primary screen reader usage."

• Provide a detailed description directly on the page, ideally near the image. This can be:
  • A table of the data immediately following the image
  • A paragraph immediately following the image
  • A collapsible “More Info” or “Data Description” section
  • A clearly labeled section within the content that explains the image in full

The above alt text identifies the image, but it does little to help someone if they cannot perceive the image content. More helpful would be a brief summary that calls out key features of the image. For example, the above alt text could also include a brief textual summary as follows:

“Pie chart showing primary screen reader usage. JAWS is the most commonly used screen reader (40.5%), followed by NVDA (37.7%) and VoiceOver (9.7%).”

Accompanying data

When there is too much data to summarize as alt text, it is common to follow the image with a table of the data. For the example above, an accompanying data table would include the percentage data from the chart:

Providing data as a download

Providing data for a chart or graph in the page is most convenient for individuals who cannot view the image, but it is not always desirable to do so. If there is a large amount of data or it is likely that an individual may want to perform their own analysis, then providing the data as a download can be the best approach. The important consideration is how easy it is for someone who cannot view an image to view the data. Requiring a lot of extra work or time would be annoying or potentially confusing due to loss of context and would not really provide an equivalent experience.

Long descriptions for other image types

Charts and graphs are the most obvious image types that may require accompanying in-text description; however, it is important to consider other image types as well. Keep in mind that the alt text for an image is read by assistive technologies in an all-or-nothing manner. If an image contains text that is longer than a short sentence or two or is otherwise information-dense, such as a map, then it could be difficult for an individual using software such as a screen reader to make sense of the alt text. In these instances an in-text description is necessary.

Images with captions

When an image has an accompanying caption, it is still necessary to provide descriptive alt text for the image. The image alt text and visible caption should never simply repeat the caption, as they serve different purposes. Instead, it should complement the caption text by describing visual details not conveyed in the caption.

Alt text provides description of the key features of an image for individuals who cannot perceive the image content. The image caption provides a visible label with the assumption that the person reading the page or document can perceive the accompanying image. Alt text and caption work together to provide a more complete description of an image that either could on its own.

Example: Poll results

The alt text for the above figure is:

"Poll results showing percentage of Americans giving local or national schools and A or a B rating between 2004 and 2025. Local schools are consistently rated higher than national schools."

Note that the alt text does not call out specific figures from the poll results, as this would be redundant because of the caption. Instead, the overall data trend is described. This is information that is visually apparent but that would not normally be information that should be present in a figure caption. Together, the additional visual information needed by individuals who cannot perceive the graph is provided and coupled with the caption to provide the desired context for the inclusion of the image. This approach ensures that all users, including those using screen readers, can access the full meaning and data conveyed by the image—without overwhelming the alt text or the caption.