How to Write Alt Text and Why

Expanding your Audience: How to Write Alt Text and Why

ACM is committed to publishing in an accessible friendly format (https://www.acm.org/accessibility) that permits all its readers to have the content presented to them in a thorough and useful way. To carry out this mandate (https://www.acm.org/media-center/2017/september/usacm-statement-on-accessibility), ACM needs the assistance of its authors to help achieve this goal. Authors are strongly encouraged to provide “alt text” (alternate text) for floats (images, tables, etc.), in their content so that those with disabilities can be given descriptive information for these figures that are important to the work. This benefits the author as well as it broadens the reader base for the author’s work. The descriptive text will be displayed in place of an image if an image cannot be loaded, and the alt text provides in-depth float descriptions to search engine crawlers, which helps to properly index the images.

To provide access to floats, the author must create the alt text for these elements in their document. Every float should have alt text provided unless it is solely decorative.

How to write alt text

(Adopted from: https://moz.com/learn/seo/alt-text ):

Do not duplicate float caption text as it detracts from the normal flow of your article and can, potentially, confuse the reader.
Describe the float as specifically as possible. Alt text is, first and foremost, designed to provide text explanations of float images for users who are unable to see them.
Keep it (relatively) short. The most popular screen readers cut off alt text at around 125 characters, so it's advisable to keep it to that character count or less.
Use your keywords. Alt text provides you another opportunity to include your target keyword on a page, and thus another opportunity to signal to search engines that your page is highly relevant to a particular search query. While your first priority should be describing and providing context to the image, if it makes sense to do so, include your keyword in the alt text of at least one float on the page.
Avoid keyword stuffing. Focus on writing descriptive alt text that provides context to the float and if possible, includes your target keyword, and leave it at that.
Don't include “image of,” “picture of,” etc. in your alt text. It’s already assumed your alt text is referring to a float, so there's no need to specify it.
Don't forget longdesc= "". Explore using the longdesc="" tag for more complex images that require a longer description.

Additional Resources

Resources for how authors should describe their image to create the “alt text” for their float elements:

http://diagramcenter.org/table-of-contents-2.html
https://www.mathmlcloud.org/ (MathML Cloud is an open source tool that creates math content that is accessible to all readers. MathML makes mathematical equations accessible to everyone by eliminating the ambiguity of a verbal description of a picture.

Insert alt text in Microsoft Word

(Adopted from https://accessibility.umn.edu/core-skills/alt-text):

In Microsoft Word: Add your image to the Microsoft Word document. Now, choose Format > Picture from the dropdown menu (or right click on the image and select “Format picture” from the menu). Click “Alt text”, one of the options on the side bar. You will want to add the full alt text in the Description field and a shorter title in the Title field. The title can help the reader decide whether or not they want to read the full description.

Please see our instructions within the ACM Master Submission Template for version-specific instructions for Windows and MAC.

How to write alt text in LaTeX

LaTeX users can use the command \Description[<short description>]{<long description>} inside every figure, teaserfigure, marginfigure, or table environment to provide a description of the image(s) used in the figure. Unlike \caption, which is used alongside the image, \Description is intended to be used instead of the image, for example,

\begin{figure}
    \centering
    \includegraphics{voltage}
   \Description[A bell-like histogram]{A bell-like histogram centered at $0.5$~V with most measurements between $0.2$~V and $0.8$~V}
   \caption{Histogram of the measurements of voltage}
   \label{fig:voltage}
\end{figure}

Not providing a Description will generate a warning at compilation.