For images to be accessible to people who are unable to see them, they must be described using text (if informative) or hidden from assistive technologies (if decorative).
Document authoring tools such as Microsoft Word and Google Docs include an option to add Alt Text to images. This is typically accessed by right-clicking an image and selecting Alt Text from the pop-up menu. If no Alt Text option is available (as in older versions of Word), you can select Format Picture or a similar option, and look for Alt Text among the available options.
In the above image from Microsoft Word, note the “Mark as decorative” checkbox. If the image is purely decorative (i.e., not communicating any meaningful information), check this box and screen readers will ignore the image.
Alt text dialogs with title and description
Google Docs, older versions of Microsoft Word, and perhaps a few other document authoring tools, offer two fields for entering alt text, Title and Description. In these cases, the best practice is to enter alt text into the Description field and leave the Title field blank. The Description field is more widely supported by assistive technologies and is more likely to survive if the document is imported into other document formats.
Complex images such as graphs, charts, or diagrams, may contain too much information to be effectively described using alt text. See the Complex Images section of the Images page in our IT Accessibility Checklist for recommendations and resources on how best to make these images accessible.