Yup! It's exactly this. It's an accessibility feature and also should be a failsafe if an image doesn't load.
accessibility.huit.harvard.edu/describe-con...
accessibility.huit.harvard.edu
Write helpful Alt Text to describe images | Digital Accessibility
Alternative (Alt) Text is an essential part of making content accessible. When adding images, charts, icons or other graphic elements, alt text should be added to ensure your content will be accessibl...