动态验证码php

<?php
session_start();

// 生成验证码
function generateCaptcha() {
    $characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $length = 6;
    $captcha = '';
    for ($i = 0; $i < $length; $i++) {
        $captcha .= $characters[rand(0, strlen($characters) - 1)];
    }
    $_SESSION['captcha'] = $captcha;
    return $captcha;
}

// 验证验证码
function verifyCaptcha($input) {
    if (isset($_SESSION['captcha']) && $_SESSION['captcha'] === $input) {
        unset($_SESSION['captcha']); // 验证成功后清除验证码
        return true;
    }
    return false;
}

if ($_SERVER['REQUEST_METHOD'] === 'GET') {
    $captcha = generateCaptcha();
    echo "<img src='data:image/png;base64," . base64_encode(imagecreatestring(60, 30, 5, $captcha)) . "' alt='Captcha'>";
} elseif ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $input = $_POST['captcha'];
    if (verifyCaptcha($input)) {
        echo "验证成功！";
    } else {
        echo "验证失败，请重试。";
    }
}
?>