PHP implements image verification code generation and verification

PHP implements the generation and verification of image verification codes

In website development, in order to prevent malicious machine attacks or automatic registration, we often use image verification codes. verify. This article will introduce how to use PHP to generate and verify image verification codes, and give specific code examples.

1. Generate image verification code

The key to generating image verification code is to generate a random verification code string and draw it onto the picture. The following is a sample code to generate an image verification code:

<?php
session_start();

// 声明图片尺寸
$image_width = 100;
$image_height = 40;

// 创建图片资源
$image = imagecreatetruecolor($image_width, $image_height);

// 生成背景颜色
$bg_color = imagecolorallocate($image, mt_rand(200, 255), mt_rand(200, 255), mt_rand(200, 255));
imagefill($image, 0, 0, $bg_color);

// 生成验证码字符串
$chars = 'ABCDEFGHJKLMNPQRSTUVWXYZabcdefghjkmnpqrstuvwxyz23456789';
$code = '';
for ($i = 0; $i < 4; $i++) {
    $code .= $chars[mt_rand(0, strlen($chars) - 1)];
}

// 将验证码字符串保存到session中，用于验证
$_SESSION['captcha'] = $code;

// 绘制验证码文字
$font_file = 'path_to_your_font.ttf';  // 替换为你自己的字体文件路径
$text_color = imagecolorallocate($image, 0, 0, 0);  // 文字颜色为黑色
imagettftext($image, 20, 0, 10, 30, $text_color, $font_file, $code);

// 输出图片
header('Content-Type: image/png');
imagepng($image);
imagedestroy($image);
?>

In the above code, first create an image resource with specified width and height through the imagecreatetruecolor function, and then use imagecolorallocateThe function generates a background color and fills the entire image, and then uses the imagettftext function to draw the verification code string onto the image at the specified position. Finally, the generated image is output through the imagepng function.

2. Verification image verification code

Verification image verification code needs to be compared with the verification code entered by the user. The following is a sample code to verify the image verification code:

<?php
session_start();

// 获取用户输入的验证码字符串
$user_input = $_POST['captcha'];

// 获取保存在session中的验证码字符串
$server_code = $_SESSION['captcha'];

// 验证用户输入的验证码与保存的验证码是否一致
if (strcasecmp($user_input, $server_code) === 0) {
    // 验证码正确，执行相应的操作
    // ...
    echo "验证码正确";
} else {
    // 验证码错误，提示用户重新输入
    echo "验证码错误";
}
?>

In the above code, first use the session_start function to open the session, and then obtain the user through the $_POST super global array Enter the verification code string, and then use the $_SESSION super global array to obtain the verification code string saved in the session. Finally, the strcasecmp function is used to compare whether the two strings are equal. If they are equal, it means that the verification code is correct and the corresponding operation will be performed. If they are not equal, it means that the verification code is wrong and the user will be prompted to re-enter.

Through the above two pieces of code, we can generate and verify the image verification code. You can save the code that generates the image verification code as a separate file, such as captcha.php. When you need to generate a verification code, you can directly access the file. The code for verifying the image verification code can be placed on a specific form submission processing page.

I hope the sample code in this article can help you generate and verify image verification codes. Of course, in actual applications, you may also need to add some security measures, such as adding interference lines, encrypting verification codes, etc.

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