On the note of CAPTCHAs, there is a US software patent on blocking requests by presenting unsolveable CAPTCHAs[1]. Just thought that was an interesting thing.
It seems that there's plenty of prior art in unreadable captchas already
I always found Google reCAPTCHA to be pretty much unsolvable.
Unless you turn off JavaScript in the browser that is, then it becomes easy.
Which is pretty surprising, it would seem that it should work other way around - with JavaScript you should have more data points to make reliable decision.
In accordance with this patent, another possibility would be that decision is in fact more reliable but I am just associated with malicious activity ...