why are most captchas designed to be illegable?

[☦ICXCNIKA ☦]

Is it asking to much to have a legable image?

[Dev]

To avoid hacks, to strengthen website security, to prevents bots, to stop people who are posting spams

[Andy T]

It is in the understanding that bot cannot read them thus still blocked, but it is hard and impractical to write such bot not impossible.

[Arthur Dent]

About CAPTCHA word verification - http://help.yahoo.com/kb/index?page=cont...OD_MAIL_ML

Problems viewing or passing CAPTCHA verification - http://help.yahoo.com/kb/index?page=cont...OD_MAIL_ML

[who WAS #1?]

I hate the darned things.
So hard to use.
But their purpose is to prevent spam computers from answering so they have to be illegible.
But for we real humans they are sure annoying.

[Paul Jackson]

Captchas prevent automated systems (bots) from submitting forms. They are hard to read because if they are easy to read, a computer program can be designed to recognize the characters and solve the captcha.

[DunbarPappy®ϟϟ]

Computers are very good at recognizing fonts of standard use.
They are not real good at making intuitive leaps at deciphering jumbled marks, whereas humans are.

It's that difference between the two which makes CAPTCHA's useful for blocking automated bots from advancing further into a site's various server files.
The more convoluted the "letters", the greater the chance that it really is a human at the helm.