The Problem with Perceptual Hashes
The problem of hash or NN based matching is, the authority can avoid explaining the mismatch.<p>Suppose the authority want to false-arrest you. They prepare a hash that matches to an innocent image they knew the target has in his Apple product. They hand that hash to the Apple, claiming it's a hash from a child abuse image and demand privacy-invasive searching for the greater good.<p>Then, Apple report you have a file that match the hash to the authority. The authority use that report for a convenient reason to false-arrest you.<p>Now what happens if you sue the authority for the intentional false-arrest? Demand the original intended file for the hash? "No. We won't reveal the original file because it's child abusing image, also we don't keep the original file for moral reason"<p>But come to think of it, we already have tons of such bogus pseudo-science technology like the dogs which conveniently bark at police's secret hand sign, polygraph, and the drug test kit which detect illegal drugs from thin air.