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php实现验证码

2026-01-13 12:31:03PHP

PHP实现验证码的方法

使用GD库生成验证码

GD库是PHP中处理图像的扩展，可用于生成验证码图片。

<?php
session_start();
$width = 120;
$height = 40;
$image = imagecreatetruecolor($width, $height);
$bgColor = imagecolorallocate($image, 255, 255, 255);
imagefill($image, 0, 0, $bgColor);

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

for ($i = 0; $i < 4; $i++) {
    $textColor = imagecolorallocate($image, rand(0, 150), rand(0, 150), rand(0, 150));
    imagettftext($image, 20, rand(-30, 30), 10 + $i * 30, 30, $textColor, 'arial.ttf', $code[$i]);
}

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

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

使用HTML表单显示验证码

在HTML页面中显示生成的验证码图片：

<img src="captcha.php" onclick="this.src='captcha.php?'+Math.random()" style="cursor:pointer" title="点击刷新验证码">

验证用户输入

验证用户提交的验证码是否正确：

<?php
session_start();
if ($_POST['captcha'] == $_SESSION['captcha']) {
    echo '验证码正确';
} else {
    echo '验证码错误';
}
?>

增加干扰线和扭曲效果

为了增强安全性，可以添加干扰线和扭曲效果：

// 添加干扰线
for ($i = 0; $i < 5; $i++) {
    $lineColor = imagecolorallocate($image, rand(150, 255), rand(150, 255), rand(150, 255));
    imageline($image, rand(0, $width), rand(0, $height), rand(0, $width), rand(0, $height), $lineColor);
}

// 扭曲效果
$distortionImage = imagecreatetruecolor($width, $height);
imagefill($distortionImage, 0, 0, $bgColor);
for ($x = 0; $x < $width; $x++) {
    for ($y = 0; $y < $height; $y++) {
        $newX = $x + sin($y / 10) * 5;
        $newY = $y + sin($x / 10) * 5;
        $color = imagecolorat($image, $x, $y);
        imagesetpixel($distortionImage, $newX, $newY, $color);
    }
}

使用Composer包

可以使用现成的Composer包来简化验证码生成：

composer require gregwar/captcha

<?php
require 'vendor/autoload.php';
use Gregwar\Captcha\CaptchaBuilder;

$builder = new CaptchaBuilder;
$builder->build();
$_SESSION['phrase'] = $builder->getPhrase();
header('Content-type: image/jpeg');
$builder->output();
?>