How Are Alt Tags Used?
They are important because without them, Google (as well as Bing, Yahoo, and other competitors) are unable to interpret visual content beyond scanning image file names for keywords. The visually impaired would also be unable to understand your site’s graphical content, making this an important UX issue to address for all images and graphics.
Example
In WordPress, you can add and edit alternative text easily by clicking the edit button on an image:
Here is what it looks like when viewed as source code (look closely for the tag alt=”Thirteen Interactive Content Examples That Will Engage Your Audience”):
Here is another look at the HTML:
