/**
 * 开发团队：逆行者联盟
 * 官方地址：www.nxzlm.com
 * 官方客服：@QiuShuYa
 */
session_start();

$width = 120;
$height = 38;
$image = imagecreatetruecolor($width, $height);

$bgColor = imagecolorallocate($image, 242, 242, 242);
imagefill($image, 0, 0, $bgColor);

$captchaCode = '';
$chars = '23456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnpqrstuvwxyz';
for ($i = 0; $i < 4; $i++) {
    $captchaCode .= $chars[mt_rand(0, strlen($chars) - 1)];
}

$_SESSION['captcha'] = strtolower($captchaCode);

for ($i = 0; $i < 5; $i++) {
    $lineColor = imagecolorallocate($image, mt_rand(100, 200), mt_rand(100, 200), mt_rand(100, 200));
    imageline($image, mt_rand(0, $width), mt_rand(0, $height), mt_rand(0, $width), mt_rand(0, $height), $lineColor);
}

for ($i = 0; $i < 50; $i++) {
    $dotColor = imagecolorallocate($image, mt_rand(150, 250), mt_rand(150, 250), mt_rand(150, 250));
    imagesetpixel($image, mt_rand(0, $width), mt_rand(0, $height), $dotColor);
}

for ($i = 0; $i < 4; $i++) {
    $textColor = imagecolorallocate($image, mt_rand(0, 100), mt_rand(0, 100), mt_rand(0, 100));
    $fontSize = mt_rand(5, 6);
    $x = ($width / 4) * $i + 10;
    $y = mt_rand(5, 15);
    imagestring($image, $fontSize, $x, $y, $captchaCode[$i], $textColor);
}

header('Content-Type: image/png');
imagepng($image);
imagedestroy($image);