You can add an explicit Alt text description to any photo in a story. Note: Previously the Alt text was populated by the photo caption but this was not always ideal.
To add Alt text to a photo, simply open its detail view → hover the photo and click "Add Click-Through Link or Alt Text". From there you will see the form below to add Alt text.
This is available for new and existing stories.
The Alt text description will still use the photo caption if no explicit Alt text is present.
In the future, you will have the option to automatically generate Alt text descriptions powered by computer vision.