Search Engines can only crawl the images, and read the alt text. The alt text helps them to determine what the images are all about enabling people to find and understand the purpose of them, what the image is, by reading the alt text.
Have you ever done an image search in Google images? You have likely found so many images related to that topic. Google rank these images using the ALT text that is assigned to them on the website at the time of uploading them. On clicking an image, you will see the location where the image is published, and then you move to the website where it is present.
ALT tags are also visible to the website visitors and readers if for some reason their browser can’t display the image. Visually impaired readers will read this text using the screen readers making your image accessible to them. So, the ALT text plays a vital role in user experience because it tells the reader what the image is all about if it can’t be displayed due to any reason.
So, ALT text can make your site the best one for users and search engines.