[zithtar]

Only one of the words is actually known and used to verify humanness. The other is an unknown scan from a book, and after a certain number of identical entries (3?) is considered known.

[Isofarro]

That reliance on "certain number of identical entries" was used by 4Chan's gaming of the Time 100 poll in 2009. The so-called "penis attack": http://musicmachinery.com/2009/04/27/moot-wins-time-inc-lose...

[zithtar]

And I think of that every time someone mentions ReCAPTCHA