Alternative text is the written description of an image that is read out loud by screen readers, helping visually impaired users navigate the content. Also, alternative text appears in place of an image on a webpage if the image can't load on a user's screen.
To write good alternative text, describe the image as specifically as possible. Also, keep it short and avoid keyword stuffing. If you can close your eyes, have someone read the alternative text to you, and imagine a reasonably accurate version of the image, you're on the right track.
Adding alt text to images in the content editor
You can add alternative text to an image in the content editor. When you hover over the image, the "+Alt text" button will appear in the top right corner of the image. Write a description in the corresponding field and click Save.
Adding alt text to images in the Audio and the Link (curation) blocks
You can also add alternative text to images in the Single audio content block and the Link (curation) content block. When a user clicks on the "+Alt text" button, the popover appears.