What is Todd's correct verification code?

The verification code is usually sent to the mobile phone.

The verification code is usually a combination of 4 or 6 digits, numbers and letters, which is sent to the designated mobile phone by SMS or voice broadcast, and is also presented in the form of pictures on the computer side.

Another verification code is a picture generated by random numbers or symbols, and some disturbing pixels are added to the picture (to prevent OCR). Users can identify the verification code information with naked eyes, enter the form and submit it to the website for verification. Only after the verification is successful can a function be used.