<?php

  session_start();

  $table=array(

    'pic0' => '狗',

    'pic1' => '猫',

    'pic2' => '鱼',

    'pic3' => '鸟',

  );

  $index=rand(0,3);

  $value=$table['pic'.$index];

  $_SESSION['authcode']=$value;

  $filename=dirname(__FILE__).'\\pic'.$index.'.jpg';

  $contents=file_get_contents($filename);

  header('content-type:image/jpg');

  echo $contents;

?>