Image Alt Text (also known as Alternate Text) is an HTML attribute that can be added to an image, typically via your website’s content management system. This is not the same thing as the image title, which can also be edited in a website’s CMS.
Image alt text is typically best used when it briefly describes an image. The more relevant the alt text is to an image, the better your image’s chances are of appearing in a Google image search (for a relevant query, of course).
Google’s algorithm favors pages with high-quality imagery, even though search engine bots can not read text embedded in an image like they can with typical text appearing on a web page.
Image alt text, and image titles, can be keyword-optimized to enhance your website’s SEO performance. However, if you upload a generic stock photo and blindly throw your keyword in the image’s alt text and title, you are unlikely to see much of an SEO improvement from your image.
By adding unique, high-quality images to your web pages that are relevant to your keywords, while also naturally inserting keywords into the image’s title and alt text, you can expect to see an improvement in your keyword rankings.