(Microsoft certainly has been making strides to make it easier to provide alternative text.
(Yes, Microsoft has added a Decorative checkbox in Office 365 and Office 2019, but it still, sadly doesn’t do what we need it to do!)
Hopefully, Microsoft will soon realize how important this is, and give us an Artifact checkbox in the Alt Text tab.
However, one of the big challenges in creating accessible PDF files from Microsoft Office is the unfortunate lack of a way within Word and PowerPoint to indicate that an image is irrelevant. Similarly, in PDF files, we mark such images as an “artifact”. If you’re familiar with creating accessible documents and webpages, then you already know the importance of using alt attributes for images in HTML, including making the attribute blank () for those images that are decorative, redundant, or irrelevant. Today’s tip is about decorative images in Microsoft Office: whether Word or PowerPoint. We’re constantly striving to create accessibility techniques that are so easy to do that everyone who creates documents can make them a habit. Thank you, Microsoft, for listening carefully, and continuing to work with us and others in the community to strive to include everyone. Therefore, although our recipe contains many nuances that are invaluable to users of earlier versions of Office, the best advice we now can offer is to upgrade to the latest version. There are still imperfections however, we have test results from all major screen reader combinations demonstrating that, for the most part, one can now trust the Decorative checkbox to behave as expected.
Update November 2020: We’re very pleased to report that the latest releases of Office 365 have substantially improved the Decorative checkbox, and that it now works effectively both with screen readers working with Office files, as well as PDF files exported from Word. How To: Alternative Text for Decorative Images in any version of Microsoft Office