...So are they deleting the original image afterward? Are you now giving Facebook the right to advertise to you based on your nude images? What happens if someone breaks into your account? Are your nude photos of yourself visible to them? Also trusting a company expressly set up to data mine to help you prevent abuse is pretty much the fox guarding the henhouse. Facebook is meant to share. Let's hope they don't accidentally overshare.

Edit: I'm seeing the researcher saying they aren't storing an image but I'm not seeing where they say they aren't.

Edit 2: They are apparently storing a link to the image on the internet, but aren't storing the image itself, which again leads me to wonder how the hash is being generated. The image has to be uploaded to the servers at some point. Is it then deleted?