As above, what happens when a sibling tries to take a photo of their overweight brother on the beach where is the brother being photogtraphed was a sister they'd be expected to be wearing a bikini top? Can these system that "allegedly work" distinguish? Would they be required to distinguish (given Gov. has not yet specified anything beyond a soundbite)? Does it work with different skin colours, different ethnicities (will, it be required to as nothing yet specified)?
And verifying the reliability, security and vulnerability of 3rd party software to be integrated into every OS in the world is non-trivial (ownership, APIs, licensing, maintaining, etc.)
Ms Kendal on the radio this morning was confusing "already exists" with the system where known child abuse image hashing and online lookup with screen/camera monitoring/blocking. Government are glibly one moment talking about "tech already exists" one moment and next saying these companies are clever and can work out how to do it (ie it still needs developing). And previous attempts in web browsers have been a disaster, eg blocking some informative non-sexual Wikipedia web pages because an image has too much flesh colour in it.
One 3rd party was trying to show-off their system but no widespread trials, no demonstrations other than an example screen showing a blocked camera (and I can do that in photoshop in 5 mins).