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by supernes 1420 days ago
Thinking about it a bit more, systems like mCaptcha and Botpoison aren't really CAPTCHA in the strict sense - they solve a somewhat different problem than telling if there's a human at the other end, and IMO that's an important distinction to make (and doesn't necessarily make them inferior to other solutions.)

I still think PoW alone is not enough as it can be automated, albeit at a slower rate. Most of the time I worry more about low-volume automated submissions than high-frequency garbage. The real value is in the combination of factors, especially what BP call the "session and request analysis" and other fingerprinting solutions.
2 comments
realaravinth 1420 days ago
> Thinking about it a bit more, systems like mCaptcha and Botpoison aren't really CAPTCHA in the strict sense

Very true! I chose to use “captcha” because it's easier to convey what it does than, say, calling it a PoW-powered rate-limter.

> The real value is in the combination of factors, especially what BP call the "session and request analysis" and other fingerprinting solutions.

Also true. I'm not sure if it is possible to implement fingerprinting without tracking activity across the internet --- something that a privacy-focused software can't do.

I have been investigating privacy-focused, hash-based spam detection that uses peer reputation[0] but the hash-based mechanism can be broken with a slight modification to the spam text.

I would love to implement spam detection but it shouldn't compromise the visitor's privacy :)

[0]: please see "kavasam" under "Projects that I'm currently working on". I should set up a website for the project soon. https://batsense.net/about

Disclosure: author of mCaptcha.

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supernes 1420 days ago
Client-local fingerprinting is not inherently evil, just when you combine it with additional signals and decide to use it in violation of users' privacy. AFAIK it's the most reliable way to distinguish unique visitor agents, and under that use case it's far more respectful of personal information than an IP address.
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ivanhoe 1420 days ago
strictly speaking it's a rate limiter, not captcha... but frankly it's probably closer to what most ppl use captchas for these days...
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