<?php
if (!isset($_SESSION)) {
    session_start();
} //檢查SESSION是否啟動
$_SESSION['check_word'] = ''; //設置存放檢查碼的SESSION

//設置定義為圖片
header("Content-type: image/PNG");

/*
                    imgcode($nums,$width,$high)
                    設置產生驗證碼圖示的參數
                    $nums 生成驗證碼個數
                    $width 圖片寬
                    $high 圖片高
                    */
imgcode(5, 120, 30);

//imgcode的function
function imgcode($nums, $width, $high)
{

    //去除了數字0和1 字母小寫O和L，為了避免辨識不清楚
    //$str = "23456789abcdefghijkmnpqrstuvwxyzABCDEFGHIJKLMOPQRSTUBWXYZ";
	$str = "1234567890";
    $code = '';
    for ($i = 0; $i < $nums; $i++) {
        $code .= $str[mt_rand(0, strlen($str) - 1)];
    }

    $_SESSION['check_word'] = $code;

    //建立圖示，設置寬度及高度與顏色等等條件
    $image = imagecreate($width, $high);
    $black = imagecolorallocate($image, mt_rand(0, 200), mt_rand(0, 200), mt_rand(0, 200));
    $border_color = imagecolorallocate($image, 21, 106, 235);
    $background_color = imagecolorallocate($image, 235, 236, 237);

    //建立圖示背景
    imagefilledrectangle($image, 0, 0, $width, $high, $background_color);

    //建立圖示邊框
    imagerectangle($image, 0, 0, $width - 1, $high - 1, $border_color);

    //在圖示布上隨機產生大量躁點
    for ($i = 0; $i < 80; $i++) {
        imagesetpixel($image, rand(0, $width), rand(0, $high), $black);
    }

    $strx = rand(3, 8);
    for ($i = 0; $i < $nums; $i++) {
        $strpos = rand(1, 6);
        imagestring($image, 5, $strx, $strpos, substr($code, $i, 1), $black);
        $strx += rand(10, 30);
    }

    imagepng($image);
    imagedestroy($image);
}
