Thanks for your reply, Ale.

The idea would be to use the image as the 'header' image for my own personal publication on Medium, so I don't really know how I would insert the credit, or work out what Partner program revenues -if any- would correspond to it.

I don't think the header images have a way of inserting a credit and license information, but the owner would be expected to have the rights to use the image. I will get in touch with Medium themselves to ask, and let you know if they can suggest a solution.