8.1 WCAG 2.1 Success Criterion 1.1.1 − Non-text Content

All content on a website must be able to be represented in text so that it can be read by screen readers. For example, images must have a text description.

This does not need to be done for Captcha or for images that are for decoration only and do not convey meaning.

Before Rectification

Screen readers are unable to read images without meaningful text descriptions.

After Rectification

For all images, a text description that can be read by the screen reader should be included. The text description should enable the person reading the webpage to know what the image is about and what it is supposed to illustrate.

WCAG 2.1 Reference: 

https://www.w3.org/WAI/WCAG21/Understanding/non-text-content