1. Module
    1. What is alt text?
    2. When should I use alt text?
  2. Video
    1. Video Transcript

Estimated time to complete: 12 minutes


What is alt text?

Alt text is simply a text alternative to non-textual content, often an image.

Thinking back to module 1, you can likely come up with some reasons why alt text is vital to a site’s accessibility. There are indeed many reasons why alt text is important:

  • Primarily, alt text allows users with a screen reader to have this assistive technology describe the contents of the image to them. This enables users with visual disabilities who cannot see the contents of the image to access this content in an alternate way.
  • Additionally, if an image cannot load due to an error or demands on the network, alt text enables users to still receive the information conveyed in the image.
  • Similarly to the previous point, if an image’s resolution is not high enough for the details to be conveyed, or if a low colour contrast makes the image difficult to perceive, alt text provides an alternative way to access the information contained in the image.
  • Aside from accessibility reasons, alt text also helps search engines identify images and direct users to relevant pages, which can boost relevant traffic to your website.

However, the main goal of accessibility is to enable access to persons with disabilities. Alt text is a necessary addition to graphics, especially when it comes to screen readers:

Speech synthesizers with screen reader software can give the blind person spoken output of what is on the computer display. However, the synthesizer can only speak text that is displayed on the screen. The increasing use of graphics leaves the synthesizer speechless. (Coombs, Assistive technology in third level and distance education, 2000)

When should I use alt text?

One mistake alt text beginners often make is to provide alt text for every image. While the enthusiasm is appreciated, not every image needs alt text.

A good rule of thumb for alt text is to use it when the image conveys some piece of information not otherwise given textually. If the image adds meaning to the surrounding content, then that meaning must be replicated in the alt text.

Here are a few examples:

1) Image is decorative: alt text not necessary

Sculpture Locavore in Carleton quad

“Celebrations and other gatherings are frequently held in Carleton’s scenic quad. Faculty, students, and staff all enjoy the outdoor environment.”

Here, the image provides nothing more than an illustration of the text. Having a description of the image would not add much to the information provided, so alt text is not needed.

2) Information appears in text: no need for alt text

Sculpture Locavore in Carleton quad

“The sculpture Locavore by Mary Anne Barkhouse depicts a snowshoe hare on a pillar, being observed by a Western coyote.”

As the information that the image provides appears in the text itself, adding alt text describing the sculpture would be redundant.

3) Information in image that does not appear in text: alt text needed!

Sculpture Locavore in Carleton quad

“Locavore, a bronze sculpture by Mary Anne Barkhouse was installed on the Carleton University quad in 2015. The sculpture draws attention to relationships between animals in nature, and the balance of the ecosystem.”

In this context, the image provides further information on how the sculpture represents “relationships between animals”. Therefore, this information should be replicated in the image’s alt text. Possible alt text could be similar to the text in the previous example: “Locavore depicts a snowshoe hare on a pillar, being observed by a Western coyote.”

If you’re unsure whether or not to put alt text on an image, consider whether you would be missing any information if the image was not there. Whatever information you would be missing should then be added as alt text, or, if extensive, worked into the surrounding text.


Video Transcript