Essentially, what you write in the Alt Text field for each image should be a description of the image content that will describe to a blind person what it is that they are not seeing. Keeping this in mind, you can strategically include keyword-rich search terms in this description that will help people find your content via searches.
Here’s a good article on alt-text-writing (concentrating on its prime purpose of aiding the sight-impaired): https://alttexthalloffame.org/
Your alt text will be read out loud to sight-impaired users, so it’s important to make it as interesting as the rest of your text content. Even though it is also a good place to use keywords that help with search, take care not to repeat the exact same phrases over and over for the benefit of your search engine optimization.
