What is Alt Text and When to Use It

Welcome to module 3 of our accessibility training. This module will address making images accessible, with a special focus on using alt text effectively.

Alt text, or alternative text, is text that is provided as an alternative to non-textual content, such as an image. Like many components of accessible design, there are many ways in which alt text can benefit the user.

• Users with visual disabilities might use a screen-reader to assist them with accessing web content. Adding alt text to an image allows that image to be conveyed out loud by the screen reader.
• An image might not load if there is an error or the network is overloaded. Alt text allows the information in the image to still be conveyed, even if the image is not able to be loaded.
• An image with low resolution or colour contrast may not be perceivable depending on the monitor it’s displayed on, and the user. Again, alt text provides the information without the photo needing to be perceived.
• Aside from accessibility reasons, alt text also helps search engines identify your images and direct relevant traffic to your website.

A common mistake made by alt text beginners is to put alt text on every single image. There are actually a few situations where images should not be given alt text. 

The general rule of thumb is that alt text should convey the meaning of the image. If the image does not add meaning to the surrounding content, or if that meaning is already stated in the surrounding text, then alt text is unnecessary. 

To help illustrate this rule, let’s look at an image in a few different contexts. Take a moment to consider this image. There are several elements that could be important, depending on the context: the sculpture, the gathering of people, even the greenery. Which of these should go in alt text, as well as whether or not alt text is actually needed depends on context.

Here is an example of content that this image might be placed next to: “Celebrations and other gatherings are frequently held in Carleton’s scenic quad. Faculty, students, and staff all enjoy the outdoor environment.”

In this case, the image provides nothing more than an illustration of the text. Having a description of the image, such as “Carleton’s quad” would not add much to the meaning of the content, so no alt text is necessary.

Alt text is also unnecessary if the information or meaning that the image conveys is already represented in the text itself. For example, if this image were placed with text that read: “The sculpture Locavore by Mary Anne Barkhouse depicts a snowshoe hare on a pillar, being observed by a Western coyote,” then repeating a description of the sculpture would be repetitive. As the meaning that the image provides appears in the text itself, alt text is not necessary in this case.

The previous two examples showed situations where alt text was not needed. However, you are sure to also encounter situations where the image does need alt text. In the simplest terms, an image needs alt text when it conveys information or meaning not already represented in the surrounding content. 

Here is one example of a situation where alt text would be needed. The surrounding text reads: “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 situation, the image provides additional, relevant information to the text, namely how the sculpture depicts relationships between animals. Therefore, alt text containing this information needs to be added. For example, the alt text could read something like: “Locavore depicts a snowshoe hare on a pillar, being observed by a Western coyote.”

Though it can sometimes be challenging to distinguish whether or not a situation calls for alt text, you can always return to the rule of thumb: any information that would be missing if the image was removed should be included as alt text or worked into the surrounding text.