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php实现图形验证码

2026-01-29 07:23:11PHP

生成随机验证码字符串

使用rand()或mt_rand()函数生成随机数字，或结合chr()函数生成随机字母。验证码长度通常为4-6位：

$length = 4;
$code = '';
$charset = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';
for ($i = 0; $i < $length; $i++) {
    $code .= $charset[rand(0, strlen($charset) - 1)];
}
$_SESSION['captcha'] = $code; // 存储到SESSION

创建图像资源

使用GD库创建画布并设置背景：

$width = 100;
$height = 30;
$image = imagecreatetruecolor($width, $height);
$bgColor = imagecolorallocate($image, 255, 255, 255);
imagefill($image, 0, 0, $bgColor);

添加干扰元素

增加干扰线或干扰点提高安全性：

// 干扰线
for ($i = 0; $i < 5; $i++) {
    $color = imagecolorallocate($image, rand(0, 255), rand(0, 255), rand(0, 255));
    imageline($image, rand(0, $width), rand(0, $height), rand(0, $width), rand(0, $height), $color);
}

// 干扰点
for ($i = 0; $i < 50; $i++) {
    $color = imagecolorallocate($image, rand(0, 255), rand(0, 255), rand(0, 255));
    imagesetpixel($image, rand(0, $width), rand(0, $height), $color);
}

绘制验证码文本

将生成的验证码字符串绘制到图像上：

$textColor = imagecolorallocate($image, 0, 0, 0);
$font = 5; // 内置字体
imagestring($image, $font, 30, 8, $code, $textColor);

// 若使用TTF字体
// $fontFile = 'path/to/font.ttf';
// imagettftext($image, 20, 0, 10, 25, $textColor, $fontFile, $code);

输出图像

设置HTTP头并输出图像：

header('Content-type: image/png');
imagepng($image);
imagedestroy($image);

完整示例代码

session_start();

$length = 4;
$charset = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';
$code = '';
for ($i = 0; $i < $length; $i++) {
    $code .= $charset[rand(0, strlen($charset) - 1)];
}
$_SESSION['captcha'] = $code;

$width = 100;
$height = 30;
$image = imagecreatetruecolor($width, $height);
$bgColor = imagecolorallocate($image, 255, 255, 255);
imagefill($image, 0, 0, $bgColor);

for ($i = 0; $i < 5; $i++) {
    $color = imagecolorallocate($image, rand(0, 255), rand(0, 255), rand(0, 255));
    imageline($image, rand(0, $width), rand(0, $height), rand(0, $width), rand(0, $height), $color);
}

$textColor = imagecolorallocate($image, 0, 0, 0);
imagestring($image, 5, 30, 8, $code, $textColor);

header('Content-type: image/png');
imagepng($image);
imagedestroy($image);

验证用户输入

在表单提交处理页面验证：

php实现图形验证码

session_start();
if ($_POST['captcha'] === $_SESSION['captcha']) {
    echo '验证码正确';
} else {
    echo '验证码错误';
}
unset($_SESSION['captcha']); // 验证后销毁