Individuals who cannot see images in Microsoft Word documents rely on the author to provide alternative text to describe the content of an image. The alternative text used should describe important aspects of the image, but be brief enough to not overburden the user. When a screen reader encounters an image in a Word document, the alternative text will be read out to the user, helping them understand what's going on in the image.
To add alternative text to an image in Word:
In the "Description" field, enter a description of the image.
If you have a detailed image that requires a long description, you may want to enter a brief summary of the description in the "Title" field. This allows users to decide if they need the full description of the image or not. Otherwise, you can leave the "Title" field blank.
For more about creating alternative text for images, see General guidelines for creating accessible documents.