Earlier quoted context omitted.
Apparently, the National Center for Missing and Exploited Children provides ISPs with a hash database of known illegal images [1]. ISPs are then required by statute to notify the government when images with matching hashes cross their network [2]. [1] https://www.law.cornell.edu/uscode/text/18/2258C [2] https://www.law.cornell.edu/uscode/text/18/2258A
While good, sort of scary because a lot of small players would host ads to get revenue and some of the ads would be filed with sexual content, even though these websites aren't even porn sites. Just some random humor site or some fortunate teller site, so if this were really true, wouldn't we be be looked at!?
That said, the UK equivalent, the IWF (Internet Watch Foundation) effectively blacklisted Wikipedia, because of the Scorpions' album cover: https://en.wikipedia.org/wiki/Internet_Watch_Foundation_and_...