> But this software doesn’t make arrests? A comparison would be police asking for what cellphones were in an area. There should be a lot of due process that happens before anything comes of this. I imagine police won’t look into one photo, they would want to match more than one.

I doubt they need, or want to match more than one. They'll use the reasoning that it only catches already-known child pornography, and that that person might have a whole cache of novel child pornography. Just look at the drug wars and how many people get arrested for trivial quantities of marijuana. And we hate child pornography way more than drugs.

> As long as there’s due process and a presumption of innocence, I’m all in favour of making it harder for criminals to get away with crimes.

The judicial system has a presumption of innocence. No one else does, or has any requirement to. The court of public opinion will ruin your life regardless of whether it's true or not.

That would be far less concerning if active cases were sealed, and only published if the defendant was ruled guilty.

> That all said… child porn is really, really terrible and I’m actually in favour of this.

I have a slight disagreement with this. The production of child pornography is obviously abhorrent. This system does nothing to stop that though, because it can only flag already-known child pornography.

This system stops the consumption of already produced and documented child pornography. While it's far outside my own interests, I can see some validity to the argument that consumption is of far less concern because it doesn't directly involve any abuse. The abuse has already happened, and no amount of tracking down pedophiles is going to reverse that. There are second order effects, like potentially reducing the demand for novel child pornography, though. Which leads me to this:

> But what other options do we have to stop these sort of crimes when the kids involved can’t or won’t speak up?

I would imagine this is far more likely to affect consumers than producers. In the drug market, stop and frisk is far more likely to net you users than producers or dealers. For one, there are more users than dealers/producers. For two, dealers, but particularly producers, are typically far more cautious than users.

That's a long-winded way of saying again that this doesn't seem likely to do much in the way of stopping people from abusing children.

But to directly answer your question: doing nothing is absolutely a valid option here. We do that for lots of bad things that happen when the costs of the solution are unbearable. It's what we're currently doing for famine in other parts of the world, which almost surely impacts more children than child pornography could even dream of doing. It's what we do for cars, which again, almost certainly impacts more children than child pornography does.

We wait until we can find a method with benefits commensurate to its costs. A 2016 DoJ report said that since 2002, 10,500 victims have been located and identified by law enforcement. That's 750 per year. There are 74 million children under 18 in the US, so that's 0.001% of children per year. 10,500 people is only 200 people higher than died from "accidental suffocation and strangling in bed" over the same period according to the CDC. The scale of the problem is the same, so should we go ahead and let Amazon send pings to the police if your Alexa thinks your suffocating in bed too?