Indeed. But this already has happened for most people. All non-jailbroken iphones and most Androids cannot have their bootloader unlocked, and even if they can, the stuff you can run is often still substantially controlled by Google.
Though in theory this can also be done without involving the OS at the device driver level. It's not hard to imagine a CNN running inside your display controller to detect a bbox and blur out the nudity. It'd still suck and be a middle finger to the owner, but I don't feel like this is much worse than what's already there. Given the popularity of porn, I can easily imagine this sparking a general public sentiment against all this nonsense.
Or, if it would break face recognition systems... (the one tattooed near the face)
No. They just want to see everything you do. Because, they will need telemetry to assess "usage". And to protect against terrorist. And to protect the children (while storing their pictures in a remote database). And...
"prevent phones from displaying nude images except when users verify that they are adults"
first were citizens, then consumers, and now users*
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