Shulou(Shulou.com)06/03 Report--

This article mainly introduces "how to realize the generation and use of .net CAPTCHA". In the daily operation, I believe that many people have doubts about how to realize the generation and use of .net CAPTCHA. The editor consulted all kinds of data and sorted out the simple and easy-to-use operation methods. I hope it will be helpful to answer the doubts about how to generate and use .net CAPTCHA. Next, please follow the editor to study!

Small class: the role of CAPTCHA:

A few years ago, most websites, forums and so on did not have CAPTCHA, because for ordinary users, CAPTCHA only increased the user's operation and reduced the user's experience. But later, all kinds of irrigation robots, voting robots and malicious registration robots emerged one after another, which not only greatly increased the burden of the website, but also brought a lot of junk data to the website database. In order to prevent the destruction of various robot programs, the programmer came up with a CAPTCHA that only the human eye can recognize, and the program is not easy to identify!

CAPTCHA is a picture with letters, numbers and even Chinese characters as the content of the picture, so that the content in a picture can be easily recognized by the human eye, but the program will not be able to recognize it. Before performing database operations (such as login verification, voting, posting, reply, registration, etc.), the program first verifies whether the CAPTCHA submitted by the client is the same as the content in the picture, and if it is the same, the database operation is carried out. Different, prompt CAPTCHA error, do not carry out database operation. In this way, all kinds of robot programs are shut out!

However, with the development of computer science, pattern recognition and other technologies become more and more mature, so the guy who writes the robot program can identify the content written directly in the picture through the program, and then submit it to the server, so the CAPTCHA will be in vain. In order to prevent the recognition of robot programs, the image generation of CAPTCHA is also developing constantly, adding interference points, interference lines, text deformation, changing angle positions, and different colors. Various techniques to prevent computer recognition are also applied to CAPTCHA. In the competition between these two technologies, the CAPTCHA we see now has been formed, and many people have complained that "what kind of CAPTCHA is this? the human eye can't tell what it is," and everything is helpless.

After understanding the function of CAPTCHA, let's write a simple example of CAPTCHA generation and use

First set up a page to display the CAPTCHA and judge whether the CAPTCHA input is correct

/ / Click the toggle verification code function f_refreshtype () {var Image1 = document.getElementById ("img"); if (Image1! = null) {Image1.src = Image1.src + "?";}}

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