When a story is published, you as the author get access to it's "Archive" page. This page will allow you to see all the photos and images from that story and download the original file you uploaded. This feature is not visible to the public. 

To access this feature, add /archive to the end of any of your story's URL to access the Archive page. It will list all your photos and images as thumbnails. From here you can click to access the original file uploaded. 

The file will open and you can then save via "Save image as" or Cmd+S.