Why do most Professional Social Network profiles fetched via the Person Profile Endpoint return a placeholder profile picture?

Our Person Profile Endpoint scrapes public Professional Social Network profiles only. And if a user does not share their profile picture publicly, then the profile picture of their public Professional Social Network profile would be a placeholder image. We cannot discern if an image is a placeholder picture or not because an image is an image. So we return the profile picture as it is – be it a placeholder or an actual user's profile picture.