Takeaway#1: Feed the Web Crawlers
Search engines, such as Google, rely on automated programs known as web crawlers that scour the web and return with information about the pages they encounter. That information influences how a page is ranked in searches and its position (higher or lower) in those results.
Like a meta tag, alt text provides one more bit of information about the web pages you create and the content you include. When you’re making a new page using a content management system (CMS), you rarely work with the HTML code itself. Rather, there’s a field for providing descriptions for the visual elements, whether photographs, illustration, charts, graphs or something else.
There are some definite do’s and don’ts for writing alt text, starting with do be specific and don’t try keyword stuffing. Check the Moz website for a thorough explanation of OK / Better / Best best practices. Put simply, your goal is to write the alt text the way you’d describe an image to a friend during a phone call.