What is the verification code of the small mobile phone?

The verification code is random and used to verify whether I operated it or not. Verification code is a public automatic program to distinguish whether the user is a computer or a person. The verification code question is generated and judged by the computer, and only humans can answer it. It can prevent malicious password cracking, ticket brushing, forum irrigation and other problems, and can be divided into Gif animation verification code, mobile phone short message verification code, mobile phone voice verification code and video verification code.