php中使用GD库做验证码

<?php require_once "string.func.php";//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){  $row="";  if($type==1){    $row=join("",range(0, 9));  }else if($type==2){    $row=join("", array_merge(range("a","z"),range("A", "Z")));  }else if($type==3){    $row=join("", array_merge(range("a","z"),range("A", "Z"),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 );}

主要要点：

1、如果前面没有申明session_start()；则需要申明；2、字体可以在cmf输入fonts下载到自己定义的fonts文件夹；3、$_SESSION [$sess_name]可以通过$_POST获得用户输入的验证码进行比较。