They can't? When you say "real headshot" are you meeting an actual picture taken with real lensing and real film and developed on photographic paper? I suspect when you say real headshot it means something that's been digitally augmented. People have become so used to their magic mirror in their phone that digitally alters their self perception that I can understand when they see other pictures that have been digitally created they may not be able to tell the difference. Perhaps it's time for a steady dose of reality so it becomes easier to identify these things.
If we thought Hollywood pretty was unrealistic for young people, just wait until we have AI pretty.
or maybe (after 5 million people choose indistinguishable-to-humans AI headshots) we'll go back to identifying posts via text handles?