Images can organize your page, emphasize your content, and make it visually appealing for visitors. With more people turning to image searches to find what they're looking for, proper image tags ensure that search engines catalog your images appropriately so people can find your site.
Because search engines can't see pictures, a keyword-rich alt attribute in an image tag gives search engines the info they need to "read" the image. Here's an example of a proper image tag with an alt attribute for a picture of a dog:
<img src="https://www.coolexample.com/dog.jpg" alt="my dog fido" />