Stick to page-relevant images – By featuring only page-relevant images, you’re making sure that crawling bots are not getting confused by their purpose.
Use the highest quality format possible – There aren’t any featured images that are of insufficient quality inside featured snippets. This should be enough to point you in the right direction.
Reduce the size of your images– Because page speed is such an important voice ranking factor, shrinking the size of your image files is crucial. Consider using tools like TinyPNG, Trimage, Optimizilla or ImageOptim.
Use captions– Captions are crawled by search engines similar to the way URLs are crawled. This means that anyone using voice keywords associated with your caption might just stumble upon your website.
Use the Alt Text attribute– There are numerous reports and clues that point towards the alt text attribute as being extremely important to voice search. Make sure to fill in the Alt Text attribute of every image that you include.
