... did you just solve the whole problem of on-going automation? Capitalism is saved! We will all work as CAPTCHA breakers. ;).
the power of paying other peole cents to fill in captchas
Similarly for VPNs and other tools. Whose use is fairly likely to increase as people start seeking ways to avoid ubiquitous surveillance.
There are other options, including a few tools that look at how to provide a fair and anonymous reputation system for Tor clients:
This was a problem before Tor anyhow. You can run a proxy for a few cents a day.
I just don't see how captchas are some awesome solution. In any anti-bot technology, the cost to circumvent it is pennies. It strikes me more as something like DRM which just makes content producers feel good, but really only punishes average people.
edit: sorry I hadn't read your links. Good points and hopefully someone like CloudFlare would make this easy for people to add to their sites.
Sorting a mechanism for allocating those tokens' seed values is difficult. FAUST requires an unblinded token request initially.
CAPTCHAs had been useful, though always problematic. The goal isn't perfection but costs. Problem is that costs keep falling.
There's an annoying triangle here: wanting to preserve privacy (== unlinkability), machine-independence, and "working well for good traffic with limited resources, as well as blocking attackers with substantially more resources". Ideally it is "choose zero", I'd be happy if the state of the art were even at "choose one".
Specifically one way to rate limit would be a cookie value that changes on each request, the previous cookie value expires, and only the site knows what the next valid cookie value is. Bots will pay for the cost of waiting in terms of computing time, and in terms of memory if they get around this by parallelization. As these costs go down due to cheaper computers, then so too will the costs of serving the site.