> HASH of a document for unlawful material This is ~super common with things like copyright violations and child porn. You store a database of hashes of copyri

> HASH of a document for unlawful material This is ~super common with things like copyright violations and child porn. You store a database of hashes of copyrighted or pornographic data. And specifically you can use visual-similarity hashing to detect even somewhat perturbed documents. (https://en.wikipedia.org/wiki/PhotoDNA https://en.wikipedia.org/wiki/PhotoDNA)