The image thumbnail called a Twitter Card that appears in Tweets is created and handled on Twitter using information from your store. Social Autopilot sends Twitter the product/blog link, so the app is not involved in the creation of the card or able to change it.
A good way of testing if your Twitter Card should work is by using this Shopify article below. Most themes should already have the code you need installed, but it never hurts to check.
Visit Using Twitter cards (links to Shopify) for more information on this.