To set an image as featured in your Medium story, user the featured image picker when you publish the post or select the image manually and press:
- Mac: ⌘ + Opt + 8
- PC: Ctrl + Alt + 8
- Or Shift + F
To set a focal point, press Alt / Opt and click. The resulting green circle will serve as a focal point for automatic image cropping that appears in post listings and previews around the site.