/**   * 验证码类，用于产生各种验证码   */  class captcha{            /**       * 生成验证码       * @param int $length 码字符长度       * @param int $width 宽度       * @param int $height 长度       * @param string $type 类型       * @return        */      public static function getCode($length=4,$width=50,$height=22,$type='png')       {          //session_start();          $randval = self::randString($length);          //$_SESSION['captcha']= $randval;                     $width = ($length*9+10)>$width?$length*9+10:$width;          if ( $type!='gif' && function_exists('imagecreatetruecolor')) {              $im = @imagecreatetruecolor($width,$height);          }else {              $im = @imagecreate($width,$height);          }          $r = Array(225,255,255,223);          $g = Array(225,236,237,255);          $b = Array(225,236,166,125);          $key = mt_rand(0,3);             $backColor = imagecolorallocate($im, $r[$key],$g[$key],$b[$key]);    //背景色（随机）          $borderColor = imagecolorallocate($im, 100, 100, 100);                    //边框色          $pointColor = imagecolorallocate($im,mt_rand(0,255),mt_rand(0,255),mt_rand(0,255));            //点颜色          @imagefilledrectangle($im, 0, 0, $width - 1, $height - 1, $backColor);          @imagerectangle($im, 0, 0, $width-1, $height-1, $borderColor);          $stringColor = imagecolorallocate($im,mt_rand(0,200),mt_rand(0,120),mt_rand(0,120));          // 干扰          for($i=0;$i<10;$i++){              $fontcolor=imagecolorallocate($im,mt_rand(0,255),mt_rand(0,255),mt_rand(0,255));              imagearc($im,mt_rand(-10,$width),mt_rand(-10,$height),mt_rand(30,300),mt_rand(20,200),55,44,$fontcolor);          }          for($i=0;$i<25;$i++){              $fontcolor=imagecolorallocate($im,mt_rand(0,255),mt_rand(0,255),mt_rand(0,255));              imagesetpixel($im,mt_rand(0,$width),mt_rand(0,$height),$pointColor);          }          @imagestring($im, 10, 20, 10, $randval, $stringColor);                header("Content-type: Image/".$type);          $ImageFun='Image'.$type;          $ImageFun($im);          imagedestroy($im);           return $randval;      }     }

以上是完整的生成图片验证码的方法，下面是使用该方法生成验证码：

 include "../lib/captcha.class.php";   $captcha = new captcha();   $checkCode = $captcha->getCode(4,75,32);   echo $checkCode;

最后在页面显示的效果就是这样，刷新一次重新生成一个：