> The code/network detecting this will be run on the client. So yes, a 'hash' or an equivalent will be known. They use cryptography to conceal the hash databas

> The code/network detecting this will be run on the client. So yes, a 'hash' or an equivalent will be known. They use cryptography to conceal the hash database from the users to guard it against accountability. Because of this, if they stuff the database with political or ethnically targeted images no one will be able to tell, you just have to trust that they haven't done that. Knowledge of a matching hash isn't a big barrier for another reason: Matching images are widely available. NCMEC reports that they had over 20 million matching images reported to them last year. It's a very reasonable assumption that some 4channer will helpfully troll the internet for likely illegal images and put up a large database of likely matches. False positives can also go the other way: Modify illegal images to match existing lawful images which are already in circulation. One could likely take legal hardcore pornography, crop it to make it impossible to identify the ages of the talent, add captions to falsely claim that they are under-age, tweak it to match targeted images, and submit it to the databases.