[voltagex_]

What are some good alternatives?

[joelthelion]

Given that Google still uses text-based captchas in 2014, I think we can safely conclude that they are still state-of-the art. Of course Google's captchas are a little harder to defeat than these ones :)

[dlss]

1. ReCAPTCHA does a lot more than Project Euler's captchas... or to put it another way, the "Zero day" you're talking about would be worthless vs ReCAPTCHA: http://en.wikipedia.org/wiki/ReCAPTCHA#Security

2. Google requires a verified cell phone number for most of their services at this point, with the captha basically being a way to avoid spamming text messages

"Given that people still drive cars in 2014, I think we can safely conclude that the 1908 Ford Model T is still state-of-the art"

[fantan]

I agree with everything you said but also want to add that recaptchas have been "solved" also. By google themselves actually (http://techcrunch.com/2014/04/16/googles-new-street-view-ima...).

Cars are safer now than they were in 1908 but are still one of leading cause of death. But it's the best we've got for now.