When posting to Twitter through HubSpot with a link inserted, the featured image of the Twitter post will be a Twitter card by default. To use a different featured image, change the Twitter card to a photo post.
Twitter cards display an image and a link preview. This image is automatically selected by Twitter based on the meta tags of the content being shared. Twitter does not allow users to change the image associated with a Twitter card.
To change the featured image in the social post, hover over the Twitter card and click Change to photo post.