What if I can't receive a foreign verification code at home?

It's normal that you can't receive foreign verification codes in China, because you need to open international roaming. It's normal to do it in America first and then come back. Now that you are back, you can try it on the commercial website of the corresponding American operator. If you set the login password before, you can. If you can't do this, you can only use China's mobile phone number to dial the service number of American operators and manually open international roaming.

CAPTCHA is the abbreviation of "fully automatic public Turing test to distinguish between computer and human", and it is a public fully automatic program to distinguish between computer and human.

It can prevent malicious password cracking, ticket brushing and forum flooding, and effectively prevent hackers from constantly trying to log in to specific registered users to use specific programs for violent cracking. In fact, using verification code is a popular way in many websites now, and we have realized this function in a relatively simple way. This question can be generated and judged by computers, but only humans can answer it. Because the computer can't answer the question of the verification code, the user who answers the question can be considered as human.

Introduction:

The word captcha was first put forward by luis von ahn, Manuel Bloom, Nicholas J Hope of Carnegie Mellon University and John langford of IBM in 2002. Carnegie Mellon University tried to apply for the word as a registered trademark, but the application was rejected on April 2, 20081.

A common verification code test is to let users enter characters or numbers displayed on distorted pictures. This deformation is to avoid being automatically recognized by computer programs such as Optical Character Recognition (OCR) and losing its effect. Because this test is tested by a computer, not by a human like the standard Turing test, people sometimes refer to the verification code as the reverse Turing test.

For people with mental and physical disabilities who can't see images, the alternative method is to read texts and numbers aloud by voice. In order to prevent speech from being recognized and analyzed, the content of speech will be noisy.