Alt (Alternative) Text

Alt text (short for alternative text) is a brief description added to images on websites or documents. 
It is read aloud by screen readers to describe the image for users with visual impairments and displays as text if an image fails to load due to a poor internet connection for example.

It should be brief and describe the image accurately unless the image is just for decorative purposes.

Automated Accessibility Tools can identify images with and without alt text, but cannot assess the appropriateness of the chosen text.