Captcha

基本解释

A CAPTCHA is a challenge-response test to determine that the response is not generated by a computer.
—一个验证码是质问-响应的测试以便于确定这个响应是不是被一个计算机产生的。
He gives an example: a CAPTCHA in which each letter was always formed out of the same number of pixels.
他举了一个例子：在一个验证码中，每个字母都是由一定数量的像素组成的。
Looking at things the other way around, a CAPTCHA system based on words that machines cannot read ought to be uncrackable.
从另一个角度看待事物，验证码系统基于机器无法辨认的文字，应该是牢不可破的。

For individual humans, CAPTCHA solving accuracy on popular sites was in the ballpark of just 85%.
FORBES: Those Scrambled Word Tests For Stopping Spambots Are Tough For Humans Too
As the social malware picked up steam, the captcha crackers were wildly busy earning their points.
FORBES: Social Media Brings a New Wave of Threats, Part 2
The captcha was a very effective defense and stopped the spread of Koobface in its tracks.
FORBES: Social Media Brings a New Wave of Threats, Part 2