Just to add, even if it CAN be done the way to do it would have to be cloud based anyway. I mean, right now, some poor guy at YouTube goes though videos looking just for this stuff. All day, every day, looking and watching horrific videos of cp and violent content. Its one of the few AI uses that can save, at least a few people of PTSD.
So now, will the media companies AND device companies do this on each text message and photo sent? Who would be responsible in case of Android phones? The maker or Google? What about a horny 14 year old's sending dick picks, will he be reported straight to the government and have an officer the next day? Hell, how will the government even determine who is even at fault.
The only way you could even do something like this is to have a universal ID like they have in South Korea or to buy "special" phones that have both picture sending/receiving, only phone numbers on contacts can be used or received AND a whitelist of websites. All of witch becomes moot as soon as the child uses a home or friends computer:P