How to implement CAPTCHA in php

This article mainly introduces how to implement CAPTCHA in php, which is very detailed and has a certain reference value. Friends who are interested must read it!

1. Font variant (generally distorted by algorithm, which is more representative: http://code.google.com/p/cool-php-captcha/

2. Font sticker (represented by qq CAPTCHA, which is still difficult to find on the Internet to crack qq CAPTCHA)

3, interference lines, noise points (this kind of identification is quite easy, it is easy to be automatically identified by the program)

As mentioned above, the first and second methods are more difficult to identify. Personally, I prefer the second method, which doesn't seem to be very laborious. And twisted words always feel strange. Haha, it's just a personal preference.

Implementation code:

The copy code is as follows: