Php+ajax Authentication Code Authentication User Login _php instance

Using AJAX to verify the user login is a benefit is not to refresh the jump page, plus the use of the verification code is more secure, groping to write down. Altogether three files are used:

yz.php: generate the code of PHP file, will verify the code will be in the session, for log in compared to call
index.php: HTML file for user login
logincheck.php: Verifying files that users log on to

The following one by one resolves:
yz.php File

<?php
 session_start ();

 Generate a validation code map
 Header ("Content-type:image/png");
 Long and wide
 $im = Imagecreate (44,18);
 Set background color:
 $back = Imagecolorallocate ($im, 245,245,245);
 Fill background color:
 imagefill ($im, 0,0, $back);

 Srand (Double) microtime () *1000000);
 $vcodes;
 Generates a 4-digit number
 for ($i =0 $i <4; $i + +) {
  $font = imagecolorallocate ($im, Rand (100,255), Rand (0,100), Rand (100,255 ));
  $authnum =rand (1,9);
  $vcodes. = $authnum;
  Imagestring ($im, 5, $i *10, 1, $authnum, $font);

 Add the jamming pixel for
 ($i =0 $i <100; $i + +) {
  $randcolor = imagecolorallocate ($im, Rand (0,255), Rand (0,255), Rand ( 0,255));
  Imagesetpixel ($im, Rand ()%70, Rand ()%30, $randcolor);
  
 Imagepng ($im);
 Imagedestroy ($im);

 The four-bit verification code is saved in the session, and when you log in, compare
 $_session["Vcode"]= $vcodes;
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index.php: Note, do not take $_session["Vcode" in this file, or you will take a step later, refresh to display the last Captcha

It's good to be logincheck.php in the test room.

<! DOCTYPE HTML PUBLIC "-//w3c//dtd HTML 4.01 transitional//en" "Http://www.w3.org/TR/html4/loose.dtd" >  

logincheck.php verifying files that users log on to

<?php 
 session_start ();
 Include (".. /conn/conndb.php ");
 
 Get the parameters of the POST:
 $username =$_post["username"];
 $password =md5 ($_post["password"]);
 $authCode =$_post["Authcode"];       
 
 $feedback = "no";

Compare whether the ==session in the verification code, can not be placed on the client, otherwise take incorrect value
 if ($authCode ==$_session["Vcode"]) {

   $SQL = "SELECT * from Users where Username= ' $username ' and password= ' $password ';
   $result =mysql_query ($SQL);
   $rows =mysql_num_rows ($result);
  if ($rows ==1)                       //Verify success
   $feedback = "OK";
   $_session["admin"]=true;           In order to secure the background, save the session, indicating that ADMIN is logged in for later call
  }
  
 echo $feedback;
 
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