A silly thing. As others point out, if it spreads, photos altered by it will quickly become part of the training set, and the method will be defeated.
And in general, it's an unwinnable quest: by definition, you cannot have a system that makes photos "undetectable to facial recognition without ruining them", because if another human can recognize you on a photo, then a machine can be taught to do the same.
And in general, it's an unwinnable quest: by definition, you cannot have a system that makes photos "undetectable to facial recognition without ruining them", because if another human can recognize you on a photo, then a machine can be taught to do the same.