Parsing the implementation code of dedeCMS verification code_PHP tutorial

As shown below:

Copy code The code is as follows:

$rndstring = '';
for($i=0; $i<4; $i++) $rndstring .= chr(mt_rand(65,90));
//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
$im = imagecreate(50,20);
ImageColorAllocate($im, 255,255,255);
//Background line
$ lineColor1 = ImageColorAllocate($im,240,220,180);
$lineColor2 = ImageColorAllocate($im,250,250,170);
for($j=3;$j<=16;$j=$j+3)
{
imageline($im,2,$j,48,$j,$lineColor1);
}
for($j=2;$j<52;$j=$j+(mt_rand (3,6)))
{
imageline($im,$j,2,$j-6,18,$lineColor2);
}
//Draw a border
$ bordercolor = ImageColorAllocate($im, 0x99,0x99,0x99);
imagerectangle($im, 0, 0, 49, 19, $bordercolor);
//Output text
$fontColor = ImageColorAllocate($ im, 48,61,50);
for($i=0;$i<$rndcodelen;$i++)
{
$bc = mt_rand(0,1);
$rndstring [$i] = strtoupper($rndstring[$i]);
imagestring($im, 5, $i*10+6, mt_rand(2,4), $rndstring[$i], $fontColor);
}
header("Pragma:no-cache/r/n");
header("Cache-Control:no-cache/r/n");
header("Expires: 0/r/n");
//Output a specific type of image format, the priority is gif -> jpg ->png
if(function_exists("imagejpeg"))
{
header("content-type:image/jpeg/r/n");
imagejpeg($im);
}
else
{
header("content-type:image /png/r/n");
imagepng($im);
}
ImageDestroy($im);
exit();
}
else
{
//GD is not supported, only letters ABCD are output
$_SESSION['dd_ckstr'] = "abcd";
$_SESSION['dd_ckstr_last'] = '';
header("content- type:image/jpeg/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();
}
?>

http://www.bkjia.com/PHPjc/327495.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/327495.htmlTechArticle is as follows: Copy the code as follows: ?php $rndstring = ''; for($i=0; $i4; $i++) $rndstring .= chr(mt_rand(65,90)); //If GD is supported, drawing if(function_exists("imagecreate")...