Verification code function of Qiannong cloud platform

Prevent malicious machine registration.

The role of verification code: effectively prevent this kind of problem from constantly trying to log in to a specific registered user by using a specific program brute force cracking method. In fact, verification code is a popular way for many websites now, and this function is relatively simple to implement. Although logging in is a bit troublesome, this function is still necessary and important for the community.