A figure is worth a thousand words: A scientist’s guide to alt text

Originally published for LabBites on October 18, 2023

In the past decade or so, there has been a stronger push to make aspects of the 'journal article' more accessible. We utilize colorblind friendly color palettes more often, scientists are encouraged to provide acronym tables to aid readers as they read, and, on a more structural level, journal websites have implemented more text to speech functionality that allows visually impaired people to access the scientific community's most recent findings. However, not all information is easily accessible through text to speech. Images in particular pose a challenge to accessibility. So, what is the solution?

Alt Text

Alt text, or alternative text, is meta data that is attached to images on webpages used to describe the content of an image. Screen readers utilize alt text to describe images for those that are visually impaired. Poor alt text means that visually impaired people miss out on potentially important visual content. You may think the figure legend does an adequate job informing a reader the contents of a figure, however, if you are used to seeing a figure, you may not realize just how much visual information doesn't get included.

Writing good alt text

1. Be concise
It only takes a sighted person a moment to comprehend an image. An alt text description should aim for something similar. Screen readers will often read the alt text in one chunk. If a person misses a word, they'll have to go all the way back to the beginning and listen to the whole thing again. Keeping the alt text short makes an image easier to comprehend, and if you find yourself getting too wordy, you may need to include more context in the text of the page. Speaking of context...

2. Consider the context
The textual content around your image dictates what needs to be included in the alt text. For example, figure legends often include a figure number and title, so it would be redundant to include it in the alt text. Instead, consider what information would be missing from the page if the image was not there.

3. What do people need to know?
It's easy to let alt text descriptions get out of hand, and while there are options to include lengthier descriptions, the aim of alt text is to provide the reader with a gist of what the image is for. What is the focus of an image?

All together, these guidelines act as a good baseline for constructing useful alt text.

Figures are a little more complex

Writing alt text for data and graphics is a little less straightforward than for simple images with a single subject. Data is especially difficult since there are so many elements, but, again, it's important to consider the context. Figure legends and results sections already include an interpretation of the results; important numbers and values such as statistical significance are typically included to support conclusions. The purpose of the figure itself is to allow readers to dive into the data with their own analytical skills to draw conclusions themselves. While there are many specifics to consider for each figure, Amy Cesal proposed a helpful formula:

alt = "Chart type of type of data where reason for including chart"
Then link to an accessible data source in the text.

This formula includes a brief explanation of the overall purpose of the data, and then provides the data in an accessible format like a table.

Example 1

Orange Tree Growth

More complex data can use the same formula for alt text, but it may require more context or a long description. If a long description is included, it should be indicated in the alt text.

Example 2

Figure 7. Differential abundance (DA) analysis of bacterial genera. Heatmaps of DA genera for the stabilized phase. Raw count data was log transformed for plotting. Genera denoted as uncultured or unknown are excluded. (Source: O’Hara et al. 2023, licensed under CC BY 4.0.)

alt = "Heatmap of differential bacterial genera abundance comparing A. taxiformis treated rumen to a control. Full description under the heading Figure 7 description."

Link to Figure 7 description*

*Note: For this kind of graphic, it may be useful to link to a screen readable version of this heatmap where the values are included for each color block in a table format.

Where can you include alt text?

When posting images online, many platforms already provide the option to add alt text. Twitter and Instagram have instructions on how to add alt text to images posted on their platforms, although Instagram's accessibility functions are hidden, which is less than ideal. And there is an abundance of tutorials detailing how to add alt text to images directly using HTML. But accessibility doesn't stop at social media and our own personal websites, if we want our scientific findings to be accessible to more people, journals need to implement options for alt text and image descriptions directly. Taylor & Francis are one of the few publishers that outline a method of including alt text for authors, and the American Chemical Society is taking a step forward by publishing an accessibility style guide while they work towards implementing alt text functionality in their publications. Alt text is by no means the norm, but the more we use it, the more widespread it will become, making the world of science ever more inclusive.