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Posted by Chris Morris on 02/23/07 16:34
Harlan Messinger <hmessinger.removethis@comcast.net> writes:
> David E. Ross wrote:
> > If you use a CAPTCHA, be sure to provide for the visually handicapped
> > who might be using an audio browser. CAPTCHAs even create problems for
> > the dyslexic and colorblind.
>
> They can even create problems for normally sighted people without
> perceptual disabilities. Oftentimes I have been unable to tell whether
> a particular stroke was part of a letter or part of the obfuscation.
Unfortunately for CAPTCHAs, image processing software is able to
defeat any capture that might be easy for a person to read... The
eventual consequence will be CAPTCHAs that no-one can read.
Of course, the reason they're a bad idea is encoded into their name. A
Turing test is where a human tries to distinguish between a human and
a computer. Since no computer program has passed the test, no computer
program is qualified to administer the test by definition... (and even
then it'd be the wrong test - automatic isn't necessarily spam, manual
isn't necessarily not spam)
Conversely, a very simply written spamfilter will catch >99.9% of
spam. It's nowhere near as complex a problem as email spam. The big
giveaway is unexpected URL markup in the content, but adding a few
other regex-based tests helps.
--
Chris
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