php 簡易的一個 驗證碼 生成

ini_set("error_reporting", "E_ALL & ~E_NOTICE");
session_start();
// 隨機碼的個數
$_rnd_code = 4;
for ($i = 0; $i < $_rnd_code; $i ++) {
    $_nmsg = $_nmsg . dechex(mt_rand(0, 15));
}
$_SESSION['code'] = $_nmsg;
$_width = 75;
$_height = 25;
$_img = imagecreatetruecolor($_width, $_height);
// 白色
$_white = imagecolorallocate($_img, 255, 255, 255);
$_black = imagecolorallocate($_img, 0, 0, 0);
// 填充
imagefill($_img, 0, 0, $_white);


$_flag = false;
if ($_flag) {
    // 邊框
    imagerectangle($_img, 0, 0, $_width - 1, $_height - 1, $_black);
}


// 畫線條
for ($i = 0; $i < 6; $i ++) {
    $_rnd_color = imagecolorallocate($_img, mt_rand(200, 255), mt_rand(200, 255), mt_rand(200, 255));
    imageline($_img, mt_rand(0, $_width), mt_rand(0, $_height), mt_rand(0, $_width), mt_rand(0, $_height), $_rnd_color);
}
// 隨機雪花
for ($i = 0; $i < 100; $i ++) {
    $_rnd_color = imagecolorallocate($_img, mt_rand(200, 255), mt_rand(200, 255), mt_rand(200, 255));
    imagestring($_img, 1, mt_rand(1, $_width), mt_rand(1, $_height), '*', $_rnd_color);
}
// 輸出驗證碼
for ($i = 0; $i < strlen($_SESSION['code']); $i ++) {
    $_rnd_color = imagecolorallocate($_img, mt_rand(0, 150), mt_rand(0, 150), mt_rand(0, 150));
    imagestring($_img, 5, $i * $_width / strlen($_SESSION['code']) + mt_rand(1, 10), mt_rand(1, $_height / 2), $_SESSION['code'][$i], $_rnd_color);
}
header('Content-Type:image/png');
imagepng($_img);
imagedestroy($_img);
?>