Mother of all CAPTCHAs

Came across this Slashdot story about a "true random number generator that relies on the unpredictable quantum process of photon emission." QRBG provides high-quality true random numbers through a web service for which you have to sign up.

I laughed my guts out at the CAPTCHA:



Nice. Makes sure you're a human AND of a certain type.

For all those who're racking their brains out yaar, sine ka differentiation kya hota tha (I did that too :-)), here are some hints:

• (d/dx) sin(x) = cos(x)


• (d/dx) cos(x) = -sin(x)


• sin(n*pi)=0 for all integer values of n


• cos(m*pi/2)=0 for all odd (integer) values of m