Example Analysis of PHP Imitation QQ Verification Code_PHP Tutorial

/**
* Imitation QQ verification code
*/
//Session save path
$sessSavePath = dirname(__FILE__)."/../data/sessions/";
if(is_writeable($sessSavePath) && is_readable($sessSavePath)){ session_save_path($sessSavePath) ; }
session_start();
//Get random characters
$rndstring = '';
for($i=0; $i<4; $i++) $rndstring .= chr( mt_rand(65,90));
$img_height=45; //First define the length and width of the image
$img_width=10;
//If GD is supported, draw
if(function_exists ("imagecreate"))
{
//In some cases, Firefox may request multiple times. Refreshing the page within 5 seconds will not change the session
$ntime = time();
if( empty($_SESSION['dd_ckstr_last']) || empty($_SESSION['dd_ckstr']) || ($ntime - $_SESSION['dd_ckstr_last'] > 5))
{
$_SESSION[ 'dd_ckstr'] = strtolower($rndstring);
$_SESSION['dd_ckstr_last'] = $ntime;
}
$rndstring = $_SESSION['dd_ckstr'];
$rndcodelen = strlen ($rndstring);
//Create an image and set the background color
$im = imagecreate(46,20);
ImageColorAllocate($im, 240,243,248);
//Interference line
$lineColor1 = ImageColorAllocate($im, mt_rand(174,218),mt_rand(190,225),mt_rand(217,237));
for($j=1;$j<=2;$j=$j+3)
{
imageline($im,0,$j+mt_rand(1,15),48,$j+mt_rand(1,15),$lineColor1);
}
//Output text
$fontColor = ImageColorAllocate($im, mt_rand(0,150),mt_rand(0,150),mt_rand(0,150));
for($i=0;$i<$rndcodelen;$i++)
{
$bc = mt_rand(0,1);
$rndstring[$i] = strtoupper($rndstring[$i]);
imagestring($im,mt_rand(3,5),$i *$img_height/4+mt_rand(1,5),mt_rand(1,$img_width/2), $rndstring[$i], $fontColor);
}
header("Pragma:no-cache" r"n");
header("Cache-Control:no-cache"r"n");
header("Expires:0"r"n");
//Output specific type The image format, the priority is gif -> jpg ->png
if(function_exists("imagepng"))
{
header("content-type:image/png"r"n" );
imagepng($im);
}
else
{
header("content-type:image/jpeg"r"n");
imagejpeg($im );
}
ImageDestroy($im);
exit();
}
else
{
//GD is not supported, only the letters ABCD are output
$_SESSION['dd_ckstr'] = "abcd";
$_SESSION['dd_ckstr_last'] = '';
header("content-type:image/png"r"n");
header ("Pragma:no-cache"r"n");
header("Cache-Control:no-cache"r"n");
header("Expires:0"r"n");
$fp = fopen("data/vdcode.jpg","r");
echo fread($fp,filesize("data/vdcode.jpg"));
fclose($fp) ;
exit();
}
?>