[OT] Some questions on captcha

[kiat]

Hi monks,

Some questions regarding captcha outputs...

I've seen some that are really cryptic and difficult to make out (e.g. Slashdot, Hotmail). I remember when trying to make a post at Slashdot that I had make at least four submits before getting it right.

Then there are those that consist of just numbers that are easily readable - just like normal text.

What is the difference between the two? Does the purely numeric and easily readable one work as well as the cryptic one?

And is there a Perl module that generates a captcha output?

Thanks :)

[Nevtlathiel]

You might be interersted to read merlyn's attempts to do something similar and jcwren's crack. Certainly food for thought about the best way to do something like this :)

[b10m]

CAPTCHAs are annoying, it's as simple as that. Although you might prevent the average script kiddy from automating filling out forms, it is not perfect. And then there is the issue of visually impaired people (they can't see the image).

I for one truely hate these systems, for a lot of them are just not readable at all. If I cannot fill out a form because I cannot read such a dumb picture, I skip the form altogether and go somewhere else. Besides, I love WWW::Mechanize ;)

So, before rushing into such means, see if you can't solve the itch another way. You are a Perlmonk, so there must be more than one way to do it ;) For instance, if you want to prevent comment-spam, look at systems such as b2evolution's antispam database, or linkcondom.com

[fglock]

There is Authen::Captcha.

[monkfan]

And is there a Perl module that generates a captcha output?

Perhaps Image::Magick or GD modules?
Check this out, hope it can be useful to you.

[fglock]

There is Authen::Captcha (which uses GD).

[Tanktalus]

Please excuse my ignorance, but what is "captcha"? Is this the image with text hiding in it, with squiggly lines throughout to make OCR difficult?

[ikegami]

yes

[dorward]

An easily readable one is easier to OCR.

A highly obscured one is hard for humans to decode.

(Both require some other way to allow people to prove they are human, otherwise you lock users out and can potentially get slapped with accessibility and anti-discrimination laws.)

[adrianh]

What is the difference between the two? Does the purely numeric and easily readable one work as well as the cryptic one?

No is the short answer. The evil people just plugged them into OCR packages, hence the escalation in obscurity.

See Another way to get around automated bots and Image Verification Program for some previous threads on image based captchas. Personally I find them annoying, not particularly effective and a complete pain on the accessibility front.