<?php      header("content-type:image/png");      $num = $_GET['num'];      $imagewidth=60;      $imageheight=18;      srand(microtime() * 100000);         $numimage = imagecreate($imagewidth,$imageheight);      imagecolorallocate($numimage,183,180,83);      for($i=0;$i<strlen($num);$i++){          $font = mt_rand(3,5);          $x = mt_rand(1,8)+$imagewidth*$i/4;          $y = mt_rand(1,$imageheight/3);          $color=imagecolorallocate($numimage,mt_rand(0,50),mt_rand(0,150),mt_rand(0,255));          imagestring($numimage,$font,$x,$y,$num[$i],$color);      }      imagepng($numimage);      imagedestroy($numimage);  ?>           调用方法：  <?php      session_start();      include_once 'conn/conn.php';      $pattern = '1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLOMNOPQRSTUVWXYZ';      $num = null;      for($i = 0; $i < 4; $i++) {          $num .= $pattern{mt_rand(0, 61)};      }    ?>     <div> 验证码：    <input id="lgchk" type="text" />    <img src="valcode.php?num=<?php echo $num; ?>" width="55" height="18" /> </div>