php验证码代码怎么写

<?php// 生成随机字符串$string = substr(str_shuffle('ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'), 0, 6);// 创建图像$image = imagecreate(150, 50);// 分配颜色$white = imagecolorallocate($image, 255, 255, 255);$black = imagecolorallocate($image, 0, 0, 0);// 将字符串写入图像imagestring($image, 5, 10, 10, $string, $black);// 添加干扰线for ($i = 0; $i < 10; $i++) {    imageline($image, rand(0, 150), rand(0, 50), rand(0, 150), rand(0, 50), $black);}// 添加干扰点for ($i = 0; $i < 200; $i++) {    imagesetpixel($image, rand(0, 150), rand(0, 50), $black);}// 输出图像header('Content-Type: image/png');imagepng($image);// 销毁图像imagedestroy($image);?>

// 获取表单提交的验证码$captchaResponse = $_POST['captcha'];// 获取预期的验证码$captchaExpected = 'YOUR_CAPTCHA_STRING';// 验证验证码if ($captchaResponse === $captchaExpected) {    // 验证码正确，处理表单提交} else {    // 验证码错误，显示错误消息}