When to add alt text

Alternative (Alt) Text is meant to convey the “why” of the image as it relates to the content of a document or webpage. It is read aloud to users by screen reader software, and it is indexed by search engines. It also displays on the page if the image fails to load.

Alt text should be brief and descriptive of the most important, meaningful elements of the image. Think to yourself, if someone couldn't see the image, how would you describe it to them within the context of the page?  

Sometimes the same image used in multiple places needs different alt text in each situation. If the existing alt text for an image doesn’t fit the context for a page, you can add new alt text in the Alt Override field.

If an image is purely decorative and does not add any meaningful content to the page, select the checkbox for Mark Image as Decorative, so that screen readers will skip over the image. Note that the Mark Image as Decorative option is only available for images added to components; it’s not available for images added using the Text Editor (see Adding an image).