如何在PHP表单中集成验证码验证功能

session_start(); // 开启会话

$length = 4; // 验证码长度
$width = 80; // 验证码宽度
$height = 30; // 验证码高度

$chars = 'abcdefghjklmnpqrstuvwxyz123456789'; // 验证码字符集合
$chars_length = strlen($chars);

$code = '';
for ($i = 0; $i < $length; $i++) {
  $code .= $chars[mt_rand(0, $chars_length - 1)];
}

$_SESSION['code'] = md5($code); // 将验证码保存到会话中

$image = imagecreatetruecolor($width, $height); // 创建画布
$background_color = imagecolorallocate($image, 255, 255, 255); // 设置背景颜色
imagefill($image, 0, 0, $background_color);

$fonts = ['arial.ttf', 'arialbd.ttf', 'ariali.ttf', 'arialbi.ttf']; // 设置字体集合
$font_colors = [
  imagecolorallocate($image, 55, 154, 196),
  imagecolorallocate($image, 250, 89, 84),
  imagecolorallocate($image, 200, 138, 45),
  imagecolorallocate($image, 82, 184, 76)
]; // 设置字体颜色集合

for ($i = 0; $i < $length; $i++) {
  $font = $fonts[mt_rand(0, count($fonts) - 1)];
  $font_color = $font_colors[mt_rand(0, count($font_colors) - 1)];
  imagettftext($image, 18, mt_rand(-30, 30), $width / $length * $i + mt_rand(0, 10), $height / 2 + mt_rand(-5, 5), $font_color, $font, $code[$i]);
}

header('Content-type: image/png'); // 设置验证码图片类型为png
imagepng($image); // 输出验证码图片
imagedestroy($image); // 释放内存

session_start(); // 开启会话

if ($_SESSION['code'] != md5($_POST['captcha'])) {
  echo '验证码错误';
  exit;
}