This is a great question David. Even though in non-monetized blogs some media photos are used commonly Medium has a specific rules that only 4 types of of photos legally can be used, they are free stock photos, images from Wiki commons, subscription based images, and photos/charts created by authors. Images from other sources are no allowed unless writers have permission to use. We explained them in our policy as this is our biggest problem since day one.

https://medium.com/p/26bf5a11d1da

Since some writers face hefty penalties and some even lost their accounts our editors are diligent on this matter to protect our writers. In short Medium is a is a content motorization platform that not every image can be used like other blogging sites.