Parsing the implementation code of dedeCMS verification code

Parsing the implementation code of dedeCMS verification code_PHP tutorial

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Release： 2016-07-21 15:08:11

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$rndstring = '';
for($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();
}
?>