Alt tags are placed in the code of your website to give images or other visual content descriptions that will be used by screen readers. This information describes the content of the image for those who cannot see it.
These explanations of the image should only be used if a description is necessary to understand the rest of the content on the page. Otherwise, an empty set of alt tags (no description) should be added to indicate an image is decorative, or just for looks, rather than a required part of your content.
Learn more about making images accessible