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Comment by sugarkjube | Hacker News Reader

Absolutely love it. Unusual captcha's are great.

Reminded me of this one: http://random.irb.hr/signup.php

Funny. I made a captcha challenge of calculus problems for a comment section on my personal blog page. But 5 years after college, I couldn't remember how to even do them myself so I changed it :-/

wolfram alpha can do it for you

You don't actually need much, for a form I used to get spam in I just added a "write 42 here" so anyone who actually cares to read would be able to fill it. spam fell to 0.

(for a site with a slightly higher profile this wouldn't be enough, but for a minor corner of the internet with no ill intent actually aimed at it that turned out to be enough to block the fuzzing "fill all the forms" spam)

Similarly an empty input field that is css'd to be outside the viewport is often filled by spambots but not humans. But I like the edge case UX of your idea more.

Just watch out that Chrome’s autofill doesn’t fill it in. Cost us a huge chunk of new signups until we found out. Chrome ignores autofill directives under some circumstances.

It's also visible for users with CSS overrides and/or other browser inpairments. The more I think about it the more strongly I prefer the "type 42" explicit input field.

You can label it “leave this field empty”, with a placeholder or similar - then it’s the same explicit instruction as “type 42”.

As contrasting experience, I did that (a simple math problem) on our contact form and it did NOT drop spam to zero; our spammers were too smart for that. Even an actual reCAPTCHA didn't completely eliminate it (although it mostly did, enough that it's fine for us).

The question I got was surprisingly simple: it asked to find "the least real root of the polynomial p(x) = (x+5)(x-4)(x+1)". A determined attacker can quickly hack together something with Tesseract and feed it into even GPT-3.5 to get the correct answer to questions like these.

I guess that means the captcha is doing its job, since running LLMs isn't very cheap or scalable. But any harder problem means you start filtering a significant chunk of human users. Based on the other replies to your comment, it seems that the questions at their current difficulty already stop a lot of human users, yet allow a determined attacker with the setup I described pass through easily.

I'm not sure how you'd determine the least real root to that, given all three have equally zero imaginary component.

I suppose the square root of negative infinity has the property of being unreal in several distinct ways, but yeah, the least real? I dunno /s

They of course the minimum out of the set of the real roots.

I remember an old (and now defunct) fan site who hit you with lore questions as a captcha. Though I'd guess a LLM could answer

Can I play by an audio call if I'm visually impared?

Yes, when you hear a monster roar you say BANG!

The first one I got was 7 * 7 + (-3). That’s trivial, elementary-school-level math, and did they really need LaTeX to render that?

Then I refreshed the page, and was hit with calculus involving trig functions.

Or the one on esolangs.org where you need to evaluate some random Befunge code.

after reloading a dozen times i finally got one that i could solve:

-3 * 3 + (-3) = ?

I just got one I think I can solve: 0 + 7 + 0 = ?

Where's my calculator?

Bond, Jim Bond ?

I got "find the last real zero of the polynomial..." but what does last mean? Largest? Last as the polynomial's factors are given? Something else?

Edit: oh wait. It's "least". I really have no idea then :)

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