Use GD library to do verification code in php to implement verification code function

<?php 
require_once &#39;string.func.php&#39;;
//通过GD库做验证码
/**
 *添加验证文字
 * @param int $type
 * @param int $length
*/
function buildRandomString($type=1,$length=4){
  $row=&#39;&#39;;
  if($type==1){
    $row=join(&#39;&#39;,range(0, 9));
  }else if($type==2){
    $row=join(&#39;&#39;, array_merge(range(&#39;a&#39;,&#39;z&#39;),range(&#39;A&#39;, &#39;Z&#39;)));
  }else if($type==3){
    $row=join(&#39;&#39;, array_merge(range(&#39;a&#39;,&#39;z&#39;),range(&#39;A&#39;, &#39;Z&#39;),range(0, 9)));
  };
  $row=str_shuffle($row);
  
  $row=substr($row,0,$length);
  return $row;
}
/**
 * 生成缩略图
 * @param int $type //包含数字或者英文
 * @param int $length 多少个字符
 * @param int $pixel 干扰小点的密度
 * @param int $dst_h 干扰线的密度
 * @param string //验证码在$_SESSION中的名字
 */

function verifyImage($type=1,$length=4,$pixel=0,$line=0,$sess_name = "verify"){
  //session_start();
  //创建画布
  $width = 100;
  $height = 40;
  $image = imagecreatetruecolor ( $width, $height );
  $white = imagecolorallocate ( $image, 255, 255, 255 );
  $black = imagecolorallocate ( $image, 0, 0, 0 );
  //用填充矩形填充画布
  imagefilledrectangle ( $image, 1, 1, $width - 2, $height - 2, $white );
  $chars = buildRandomString ( $type, $length );
  $_SESSION [$sess_name] = $chars;
  //$fontfiles = array ("MSYH.TTF", "MSYHBD.TTF", "SIMLI.TTF", "SIMSUN.TTC", "SIMYOU.TTF", "STZHONGS.TTF" );
  $fontfiles = array ("SIMKAI.TTF" );
  //由于字体文件比较大，就只保留一个字体，如果有需要的同学可以自己添加字体，字体在你的电脑中的fonts文件夹里有，直接运行输入fonts就能看到相应字体
  for($i = 0; $i < $length; $i ++) {
    $size = mt_rand ( 14, 18 );
    $angle = mt_rand ( - 15, 15 );
    $x = 5 + $i * $size;
    $y = mt_rand ( 20, 26 );
    $fontfile = "../fonts/" . $fontfiles [mt_rand ( 0, count ( $fontfiles ) - 1 )];
    $color = imagecolorallocate ( $image, mt_rand ( 50, 90 ), mt_rand ( 80, 200 ), mt_rand ( 90, 180 ) );
    $text = substr ( $chars, $i, 1 );
    imagettftext ( $image, $size, $angle, $x, $y, $color, $fontfile, $text );
  }
  if ($pixel) {
    for($i = 0; $i < 50; $i ++) {
      imagesetpixel ( $image, mt_rand ( 0, $width - 1 ), mt_rand ( 0, $height - 1 ), $black );
    }
  }
  if ($line) {
    for($i = 1; $i < $line; $i ++) {
      $color = imagecolorallocate ( $image, mt_rand ( 50, 90 ), mt_rand ( 80, 200 ), mt_rand ( 90, 180 ) );
      imageline ( $image, mt_rand ( 0, $width - 1 ), mt_rand ( 0, $height - 1 ), mt_rand ( 0, $width - 1 ), mt_rand ( 0, $height - 1 ), $color );
    }
  }
  header ( "content-type:image/gif" );
  imagegif ( $image );
  imagedestroy ( $image );
}