How to generate refreshable image verification code using PHP

How to use PHP to generate a refreshable image verification code

With the development of the Internet, in order to prevent malicious attacks and automatic machine operations, many websites use verification code for user authentication. One common type of verification code is the image verification code, which generates a picture containing random characters and requires the user to enter the correct characters before proceeding.

This article will introduce how to use PHP to generate refreshable image verification codes and provide specific code examples.

Step 1: Create a verification code image

First, we need to create a function for generating a verification code image. Through PHP's GD library, we can easily manipulate images. The following is a sample code for creating a verification code image:

In the above code, the generateCaptcha function is used to generate a verification code and save the verification code string to the Session. Then, create a blank verification code picture, set the background color, text color, font and other parameters, and draw the verification code on the picture. Finally, set the output content type to image through the header function, call the imagepng function to output the image, and then destroy the image resource.

Step 2: Use the verification code image

The following is a simple sample code for displaying the verification code image on the web page and accepting the verification code entered by the user:

    
    



    

        请输入验证码：
        
        
        提交
    

In the above code, the action attribute of the form form points to a PHP file that verifies the verification code (such as verify_captcha.php), img## The src attribute of the #tag points to the PHP file that generates the verification code image (such as captcha.php). After the user enters the verification code in the input box, the form is submitted and verified.

session_start function, and then the verification code entered by the user and previously saved in the Session are obtained Verification codes are compared. If they are the same, output "verification code is correct"; if they are different, output "verification code is wrong".

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