I wonder if it is possible to check whether the request came through Tor, and not report it in that case? Bringing down exit nodes with CP reports does not seem like it would hurt the right people (only very indirectly).
Supposing I was ok with directly alerting the authorities, which for some reason seems to be perhaps a bridge too far, how would I even go about that? Where's the "report pedophiles" REST API?
OP said "API", and refers to many thousands of images which need to be evaluated. It seems like he is pointing out here that this problem is unlikely to have a completely algorithmic solution, and if it does, the solution is probably not to spam the police with tens of thousands of criminal accusations against his customers that have never been vetted by a human.
Whether or not this is moral is irrelevant if it's not scalable. How about automated flagging of images for moderator review, and thinking about ways to reward or remunerate the moderators?
CV age detection should really be a thing, if it isn't already. Maybe there's an opportunity there if it's not already done, or way too hard?
Producers and consumers of CP are not prosecuted for their thoughts, they are prosecuted for their actions. The subjects of these images suffer real and lasting psychological and physical damage.
Once again, these images don't contain meta-data stating the persons age, ages of consent are different around the world, someone can accidentally click something they didn't mean to or reasonably expected was not CP as almost the entire internet avidly sanitizes these images. I wouldn't go as far as to say it is "thought crime", but it can be non-obvious what is illegal. I am assuming the GP meant this and not that since these images already exist it is acceptable as the fantasy is in one's head, as that is not a reasonable excuse.
That argument doesn't apply here though. If someone is manually uploading an image of a child being raped to an image hosting website, there's no accident about it. Reporting someone who uploaded that image (i.e. someone who is distributing child pornography) is the only ethical and sensible option.
Now, if someone is uploading an image of their 16-year-old girlfriend taking a nude picture of themselves, that's still illegal but more of an ethical gray area, in which case I could understand hesitation at reporting to authorities. But based on OP's description, it's the real bad stuff, so reporting seems to be a no-brainer.
And I would imagine a bunch of child porn photos don't technically show anything illegal (nothing illegal about a child being naked on their own, what's illegal is the taking of the photos for sexual gratification - don't ask me exactly where the line is there, though)
It's one thing to not want to report IPs that access the image, as it could be a complete accident. But why wouldn't you want to report someone who is actively trying to share such content?
Just to provide a counterpoint, many people (myself included) believe free speech and privacy are fundamental in society, extending to the internet. Also, having a very US centric view of the world can make you forget that age of consent is arbitrary depending on where you are in the world with many european countries allowing for different laws. Also, it is quite difficult to ascertain the exact age of a subject given simply a photo. So while you are "disgusted" it is important to realize that this is a difficult problem both in identifying content and identifying perpetrators.
That being said, if it is obvious that the image is CP and you have the IP address of someone who uploaded it, I couldn't imagine not passing on that information. Also, I would put a public disclaimer on the site indicating your policy.
edit: before people start flaming me as a rape apologist I want to clarify that notifying the FBI and giving away your users public information is a strong action. It is warranted in the case of CP (one of the few things I personally think) but that, as this thread is indicative of, it is difficult to identify IRL.
People who commit crimes like this are some of the worst in the world and I am truly sorry that happened to you. As I stated, I personally think that reporting it is an absolute necessity and something that should be written into your sites policy and prominently displayed. Just to reiterate though, the issue isn't whether child porn is wrong it is how to properly identify it. If you are going to accuse someone of being a paedophile and give their information to the FBI it is important you are correct.
And I'm sure parents of murdered or otherwise killed children would be offended by reddit's "pictures of dead kids". Yet it's not illegal to share such images.
If you think it is CP you should report it, period. It's law enforcement's job to determine whether it is for sure, not you. Better to raise a false alarm or two than to let a child predator get away.