PHP验证码怎么生成_PHP验证码的生成原理与代码实现

<?php
session_start();
<p>// 验证码配置
$width = 120;
$height = 40;
$length = 4;</p><p>// 字符集（避免易混淆字符如0,O,l,1等）
$chars = '23456789ABCDEFGHJKLMNPQRSTUVWXYZ';</p><p>// 创建图像资源
$image = imagecreatetruecolor($width, $height);</p><p>// 颜色定义
$bgColor = imagecolorallocate($image, 240, 240, 240);
$textColor = imagecolorallocate($image, 0, 0, 0);
$noiseColor = imagecolorallocate($image, 150, 150, 150);</p><p>// 填充背景
imagefill($image, 0, 0, $bgColor);</p><p>// 生成随机验证码
$code = '';
for ($i = 0; $i < $length; $i++) {
$char = $chars[mt_rand(0, strlen($chars) - 1)];
$code .= $char;</p><pre class='brush:php;toolbar:false;'>// 字体大小和位置随机
$fontSize = mt_rand(14, 18);
$x = intval($width / $length * ($i + 0.3));
$y = mt_rand(20, 25);

// 绘制字符
imagestring($image, $fontSize, $x, $y, $char, $textColor);

&ltp&gt
    &ltlabel&gt验证码：&ltinput type="text" name="captcha" /&gt&lt/label&gt
    &ltimg src="captcha.php" alt="验证码" onclick="this.src='captcha.php?'+Math.random()" style="cursor:pointer;" /&gt
&lt/p&gt

if (isset($_POST['captcha'])) {
    if ($_POST['captcha'] == $_SESSION['captcha']) {
        echo "验证成功";
    } else {
        echo "验证码错误";
    }
}