Discuss how to extract verification code in php168_cms_PHP tutorial

function yzImg($nmsg){
if (function_exists('imagecreatetruecolor')){
$imstr[0]["s"]=$nmsg[0];
$imstr[1]["s"]=$nmsg[1];
$imstr[2]["s"]=$nmsg[2];
$imstr[3]["s"]=$nmsg[3];
//文件头...
header("Content-type: image/png");
//创建真彩色白纸
$im = @imagecreatetruecolor(50, 20) or die("建立图像失败");
//获取背景颜色
$background_color = imagecolorallocate($im, 255, 255, 255);
//填充背景颜色(这个东西类似油桶)
imagefill($im,0,0,$background_color);
//获取边框颜色
$border_color = imagecolorallocate($im,200,200,200);
//画矩形，边框颜色200,200,200
imagerectangle($im,0,0,49,19,$border_color);
//逐行炫耀背景，全屏用1或0
for($i=2;$i<28;$i++){
//获取随机淡色
$line_color = imagecolorallocate($im,rand(180,255),rand(180,255),rand(180,255));
//画线
imageline($im,2,$i,47,$i,$line_color);
}
//设置字体大小
$font_size=12;
//设置印上去的文字
$Str[0] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
$Str[1] = "abcdefghijklmnopqrstuvwxyz";
$Str[2] = "01234567891234567890123456";
//获取第1个随机文字
//$imstr[0]["s"] = $Str[rand(0,2)][rand(0,25)];
$imstr[0]["x"] = rand(2,5);
$imstr[0]["y"] = rand(1,4);
//获取第2个随机文字
//$imstr[1]["s"] = $Str[rand(0,2)][rand(0,25)];
$imstr[1]["x"] = $imstr[0]["x"]+$font_size-1+rand(0,1);
$imstr[1]["y"] = rand(1,3);
//获取第3个随机文字
//$imstr[2]["s"] = $Str[rand(0,2)][rand(0,25)];
$imstr[2]["x"] = $imstr[1]["x"]+$font_size-1+rand(0,1);
$imstr[2]["y"] = rand(1,4);
//获取第4个随机文字
//$imstr[3]["s"] = $Str[rand(0,2)][rand(0,25)];
$imstr[3]["x"] = $imstr[2]["x"]+$font_size-1+rand(0,1);
$imstr[3]["y"] = rand(1,3);
//写入随机字串
for($i=0;$i<4;$i++){
//获取随机较深颜色
$text_color = imagecolorallocate($im,rand(80,180),rand(80,180),rand(80,180));
//画文字
imagechar($im,$font_size,$imstr[$i]["x"],$imstr[$i]["y"],$imstr[$i]["s"],$text_color);
}
//显示图片
imagepng($im);
//销毁图片
imagedestroy($im);
exit;
} else {
header("Pragma:no-cache");
header("Cache-control:no-cache");
header("ContentType: Image/BMP");

$Color[0] = chr(0).chr(0).chr(0);
$Color[1] = chr(255).chr(255).chr(255);
$_Num[0] = "1110000111110111101111011110111101001011110100101111010010111101001011110111101111011110111110000111";
$_Num[1] = "1111011111110001111111110111111111011111111101111111110111111111011111111101111111110111111100000111";
$_Num[2] = "1110000111110111101111011110111111111011111111011111111011111111011111111011111111011110111100000011";
$_Num[3] = "1110000111110111101111011110111111110111111100111111111101111111111011110111101111011110111110000111";
$_Num[4] = "1111101111111110111111110011111110101111110110111111011011111100000011111110111111111011111111000011";
$_Num[5] = "1100000011110111111111011111111101000111110011101111111110111111111011110111101111011110111110000111";
$_Num[6] = "1111000111111011101111011111111101111111110100011111001110111101111011110111101111011110111110000111";
$_Num[7] = "1100000011110111011111011101111111101111111110111111110111111111011111111101111111110111111111011111";
$_Num[8] = "1110000111110111101111011110111101111011111000011111101101111101111011110111101111011110111110000111";
$_Num[9] = "1110001111110111011111011110111101111011110111001111100010111111111011111111101111011101111110001111";

echo chr(66).chr(77).chr(230).chr(4).chr(0).chr(0).chr(0).chr(0).chr(0).chr(0).chr(54).chr(0).chr(0).chr(0).chr(40).chr(0).chr(0).chr(0).chr(40).chr(0).chr(0).chr(0).chr(10).chr(0).chr(0).chr(0).chr(1).chr(0);
echo chr(24).chr(0).chr(0).chr(0).chr(0).chr(0).chr(176).chr(4).chr(0).chr(0).chr(18).chr(11).chr(0).chr(0).chr(18).chr(11).chr(0).chr(0).chr(0).chr(0).chr(0).chr(0).chr(0).chr(0).chr(0).chr(0);

for ($i=9;$i>=0;$i--){
    for ($j=0;$j<=3;$j++){
for ($k=1;$k<=10;$k++){
echo $Color[substr($_Num[$nmsg[$j]], $i * 10 + $k, 1)];
}
}
}
exit;
}

}

$string_yzimg=yzImgNumRand(4);

yzImg($string_yzimg);

function yzImgNumRand($lenth){
mt_srand((double)microtime() * 1000000);
for($i=0;$i<$lenth;$i++){
$randval .= mt_rand(1,9);
}
return $randval;
}
/*==Hermit Bird==*/
?>

function yzImgNumRand($lenth) {
mt_srand((double)microtime() * 1000000);
$Str[0] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
$Str[1] = "abcdefghijklmnopqrstuvwxyz";
$Str[2] = "01234567891234567890123456";
for($i=0;$i<$lenth;$i++){
$randval.= $Str[rand(0,2)][rand(0,25)] ;
}
return $randval;
}