You're never getting permission to use photos/screenshots of someone committing an offense, so there's a news exclusion for photos/videos that serve a news purpose. If an author won a significant prize using a stolen or unattributed photo and your news story reported that with a screenshot of the photo in question sans attribution for proof, that's probably allowed. If Medium changed the image, they are probably aware of some problem or wrongdoing, which is interesting.

Author of “The Moldavite Message.” Seeker, traveler, birder, crystal collector.