The alt attribute provides an alternative text in case the browser can't load the image. It also allows search engines to index your content, which means that your images will show up on the search page results when users mention keywords from their alt text.

Keep your alt text less than 125 characters as many screen readers stop reading after that.^[1]There's no need to say "picture of..." or "image of..." as assistive technologies will announce it anyway — jump right into the description and try to be specific.