Picture Captions
Providing diagrams or pictures with captions allows your readers to know what it is they are looking at. Screen reader software can read the caption and help visually impaired readers know what is there. Adding images with captions also provides readers with a means to orientate themselves in the text.
You can add captions within Word and use these captions to generate a list of illustrations which may be useful if you are producing a lengthy document.
References and Techniques
Appropriate Captioning (JISC TechDis)
Office 2010
Word 2010: Add captions in Word