Document features such as images cannot be understood by the user of a screen reader unless they have associated alternative text. Therefore, it is necessary to define an alternative text to make sure that the graphic is accessible.
The accessibility is dependent on the inclusion of a variety of semantic information, such as alternative text for image which is a kind of descriptive metadata. Alternative text is used to describe graphics and their contexts, and its primary purpose is to describe the graphic to visitors who are unable to see them.
When including alternative text, you ensure that all users can appreciate the content.
When writing alternative text, strive to be informative, not poetic, and remember that brief is better. Use complete sentences with proper punctuation and check your spelling. Do not include any information that is already present in the caption.