Captcha

基本解釋

A CAPTCHA is a challenge-response test to determine that the response is not generated by a computer.
—一個驗證碼是質問-響應的測試以便于確定這個響應是不是被一個計算機產生的。
He gives an example: a CAPTCHA in which each letter was always formed out of the same number of pixels.
他舉了一個例子：在一個驗證碼中，每個字母都是由一定數量的像素組成的。
Looking at things the other way around, a CAPTCHA system based on words that machines cannot read ought to be uncrackable.
從另一個角度看待事物，驗證碼系統(tǒng)基于機器無法辨認的文字，應該是牢不可破的。

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