That example is easy to solve because it is not using any of the provided techniques that makes it more difficult for robots to solve the CAPTCHA: "changing the HTML background color based on: mouse cursor hovering, previous state or input or shared secret"
The purpose of the example is to give you a basis on which you could implement an effective CAPTCHA.
The claim of "difficult or even completely impossible for robots" applies to CAPTCHAs using the above techniques, which are not used in the example.
Comments
The first can be proven with the provided benchmarking tool.[1]
As for the second, I agree that the source of those "units sold" should be cited.
[1]http://gwan.ch/source/ab.c
Ok for far fetched statement here is this: https://gist.github.com/2932918
They claim their algorithm is impossible to solve using robots... When it is obvious that it isn't impossible...
That example is easy to solve because it is not using any of the provided techniques that makes it more difficult for robots to solve the CAPTCHA: "changing the HTML background color based on: mouse cursor hovering, previous state or input or shared secret"
The purpose of the example is to give you a basis on which you could implement an effective CAPTCHA.
The claim of "difficult or even completely impossible for robots" applies to CAPTCHAs using the above techniques, which are not used in the example.