Accessibility FAST

Alternative Text
Quick Start Guide

Alternative text (alt text) is an equivalent text description of visual information.

Text equivalent, Figure caption, or Alt text

Visual content that conveys information needs to be described in text. There are three methods to provide descriptions in:

Adjacent text. Provide a text equivalent to visuals in an adjacent paragraph. Use visuals and text to support and reinforce each other. All users can access information in their preferred format.

Figure captions placed below visual elements are useful to orient users, link to additional information, and provide an accessible text equivalent to visual information.

The alt text field is read by screen reader software used by blind and visually impaired users. Alt text is displayed if an image is blocked or the source is missing.

Alt text can be repeated in multiple formats. However, if equivalent information is present in adjacent text or a figure caption, a visual should be marked as decorative.

To get started with alt text:

Mark decorative images

Alt text depends on context and purpose. Images included for purely aesthetic purposes, or that have an adjacent text equivalent or figure caption, should be marked as decorative.

If unsure, err on the side of adding alt text. It is better to present information twice than have someone miss out completely.

Describe informative images

Alt text is read by screen reader software to blind and low-vision users. Use alt text tools to include a brief description of visual content that presents information.

Marking images as decorative, adding a figure caption, or including alt text will differ depending on platform or software. Refer to later chapters in this guide cover providing text equivalents to visuals in specific platforms.


Use type + focus + details

To write alt text: Include the type of visual, describe the focus, and add essential details. Consider how you would describe the image if talking to a friend on the phone. Use proper punctuation and grammar and limit alt text to 2 or 3 brief sentences.

Alt Text Example

Diagram of satellite image resolutions comparing real object shape to 30 metre, 10 metre, and 1 metre resolution images. The diagram explains that as the resolution of a satellite image increases the image will more accurately represent the true shape of an object.[type] Diagram of [focus] satellite image resolutions comparing real object shape to satellite images taken at 30 metre, 10 metre, and 1 metre resolutions. [details] The diagram illustrates that the shape of an object will be more accurately represented as the resolution of a satellite image increases.

Use AI as a starting point

AI has rapidly improved in describing images, particularly the structure of complex images and extracting text from images. Edit AI generated descriptions for accuracy and clarity. Read more about using AI to generate alt text.


Moving forward…

Understand that alternative text is so fundamental to accessibility it is the first Web Content Accessibility Guideline (1.1.1). Writing alt text is somewhat of an art. Remember to try your best, ask for help, and try to be as inclusive as possible.

For more information on Alt Text, move to the next page.


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Accessibility Handbook for Teaching and Learning Copyright © 2023 by Briana Fraser and Luke McKnight is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.