> a human verifying the images would dismiss the false positive

How is a human supposed to distinguish that a visual derivative (a low res sobel filtered image, presumably) of ordinary, lawful, adult pornography isn't child porn when the system has already identified it as such?

I agree that using real child porn is an attack too, but at least in that case you could say the system was doing as designed (even though what its doing shouldn't be something that we want) ... but it's not even guaranteed to do as designed.