I did once accidentally click on a link that took me to a 'real rape videos' site that started playing a sample. That it was clearly as real as the Daily Mail's view of the world was obvious in seconds. If you were an unsuspecting woman wandering around the house, you would be asking what the camera crew were doing following you around and pointing the camera meaningfully at the window the 'rapist' was about to come through. It didn't help that a reflection during a 'point of view' shot, looking in at her, showed it was the same crew, doing another shot possibly days earlier or later. Ban that, and you need to lose The Accused (1988) and much else.
The Chinese have text based ban lists. At least one has been leaked, so we can see that they're pretty odd even allowing for machine translation. But doing text matching on searches and results is simple.
Here, the technically illiterate PM and media supporters imagine there is a way to automatically know if an image or video could be classified as unacceptable (to whom?) This is harder, to put it mildly. If the ISPs and search engines have any balls, they will be asking for a precise unambiguous programmable definition of what to ban - rather than 'stuff I don't like' which is what it appears to be at the moment - with a guarantee that they will be indemnified against damages for 'false positives'. The government will either fail totally to come up with it or they will solve several major problems in Artificial Intelligence. Either way, result!
Even with text, there are problems. Ban a word or phrase and people use other ones. (It's probably why the Chinese lists are so weird - they're trying to keep up with an evolving target). I am hoping that 'conservative' becomes the new code word for porn, and such searches get banned. Before that happens, do they really want to ban searches for 'block child porn' because of the last two words?
I'm sure I've told the story about how an internet kiosk at my ex-work - a project for male and trans sex workers - blocked the entire bbc.co.uk site because somewhere on it was the word 'breasts'.