Sean O'Hara says:

Why not give photo captchas a try — “Which of these pictures is a kitten?” followed by photos of a puppy, calf, doe, and kitten.

SomeDudeOnTheInternet says:

reCAPTCHA

Jeff says:

This brings back some memories…
source: http://en.wikipedia.org/wiki/Riemann_hypothesis

“The Riemann hypothesis (also called the Riemann zeta-hypothesis), first formulated by Bernhard Riemann in 1859, is one of the most famous and important unsolved problems in mathematics. It has been an open question for almost 150 years, despite attracting concentrated efforts from many outstanding mathematicians. Unlike some other celebrated problems, it is more attractive to professionals in the field than to amateurs.

The Riemann hypothesis (RH) is a conjecture about the distribution of the zeros of the Riemann zeta-function ζ(s). The Riemann zeta-function is defined for all complex numbers s ≠ 1. It has zeros at the negative even integers (i.e. at s = −2, s = −4, s = −6, …). These are called the trivial zeros. The Riemann hypothesis is concerned with the non-trivial zeros, and states that:

The real part of any non-trivial zero of the Riemann zeta function is ½.

Thus the non-trivial zeros should lie on the so-called critical line, ½ + it, where t is a real number and i is the imaginary unit. The Riemann zeta-function along the critical line is sometimes studied in terms of the Z-function, whose real zeros correspond to the zeros of the zeta-function on the critical line.

The Riemann hypothesis is one of the most important open problems of contemporary mathematics, mainly because a large number of deep and important other results have been proven under the condition that it holds. Most mathematicians believe the Riemann hypothesis to be true.[1] A $1,000,000 prize has been offered by the Clay Mathematics Institute for the first correct proof.[2]”

noname says:

What is wrong with the current system?

Will this deny robot like readers and encourage people who have something intelligent even thoughtful to add?

I am all for it, even if it keeps me from posting lame comments.

BubbaRay says:

#13, There are 7 girls “in” a bus. How many legs are there “on” the bus? I don’t know, I can’t see the top of the bus, or its floor either.

Another “gotcha” in the problem is “for every big cat there are 7 little cats.” OK, but are they in the backpacks?

I have $2. For each dollar, there are billions more. How much do I have? $2. (Rats.)

Jim says:

So have you actually determined how many failed spamming attempts there have been that the Captcha took care of? If it’s working well why change it?

Or are spams getting through regardless and someone at DU spends all day waiting with baited breath to remove them?

In which case I’d say someone needs a life.

Misanthropic Scott says:

If you’re trying to decrease the number of stupid replies, this might help. However, it might dramatically reduce the number of replies.

Angus S-F says:

Why not combine the current distorted-letter CAPTCHA with variable instructions like “Enter the letters in reverse order”, “Enter the 1st, third, and second-from-last letter”, and so forth. It should be possible to come up with a very large set of instructions and you could even have some of the instructions as graphics rather than text so any “smart” program would also have to OCR the graphics *_and_* understand the OCRd results.

Mister Mustard says:

>>I don’t think anyone should be allowed to
>>post until they can prove the existence
>>of God.

Or disprove it.

lynn says:

If you all are trying to keep me out, you’re doing it wrong.

Just ask me, and I’ll leave quietly.