Hi,
Currently Twitter does not support sharing specific image, so we do not include that button with the other media sharing buttons. The article share button only supports customizing the message that is tweeted.
When a tweet with a link is posted to Twitter, it will crawl that site and look for images to use as the thumbnail. This can be customized by adding <meta> tags to your site’s <head>. Easy Social Share Buttons currently does not support these tags but we will look into adding this to the plugin’s development roadmap.
More information on Twitter <meta> tags can be found here.
https://developer.twitter.com/en/docs/tweets/optimize-with-cards/overview/summary-card-with-large-image
Thanks!
