Add alt text to images, such as pictures, clip art, and screenshots, so that screen readers can read the text to describe the image to users who can’t see the image.
To add alternative text to an image in Word for Mac:
Right-click anywhere on an image. Choose Add Alt Text.
When the Set Alt Text window appears, enter descriptive alternative text in the box and click “OK.”
For more hints and guidelines for writing good alt text, visit the page Writing for Accessibility: Alt Tags and Long Descriptions.