When your published post is shown on Vocal and in the community, the preview will appear with a featured image (if you've included a featured image).
The featured image is the first image that appears chronologically in your post. It appears right after your subtitle when editing. This featured image is also used when your post is linked or embedded in social media or other websites.
To change a featured image that is already uploaded in your post, simply upload another photo and hit "Save Changes".