Image alt tags are the text that sometimes appears in place of images. It is used to describe your image and make them search-friendly. When you use alt tags on your images, they become search-friendly and are more likely to appear on search results pages to visitors who are searching for them.
Default WordPress functionality allows you to alt tag images after you upload them on your website, all images show a field of title and alternative text where you can tag your images simply by describing them in brief.
There are also some free plugins that allow you to automatically alt tag your images. Auto image alt text (Alt tag, Alt attribute) optimizer for Google images is one such plugin which upon activation automatically starts adding alt text to your images uploaded on posts, pages, and also on products created on a WordPress Ecommerce installation.
The plugin is compatible with Pinterest, WooCommerce, TinyMCE, Page Builder by SiteOrigin, Elementor Page Builder, Gutenberg, Yoast, and provides you manual customization of alt tags other than those used by Yoast or page titles.
More than twenty percent of search queries are made on Google Images so if you are running a photo blog or share more images on your posts then using alt image tags is a critical step that should not be overlooked.