[tomxor]

They are effectively low resolution hashes - obviously they would be completely useless if they fail to detect a re-encoded or slightly transformed or cropped image. In this sense it's a hash with a very high collision rate... probably even higher if you limit it to innocent but otherwise visually similar image of parents and grandparents sending pictures of their own toddlers as GP describes.

This is when it gets scary, demonising people based on a hash collision with no evidence or context.