Solution to the inconsistent php session verification code and always display the last verification code

 $(".login").live('click',function(){
 var username=$(".input_user").val();
 var password=$( ".input_ps").val();
 var code=$('.input_checkcode').val();
 if(username==""){
 alert("Username cannot be empty");
 return false;
 }
 if(password==""){
 alert("Password cannot be empty");
 return false;
 }
 var URL="checkLogin.php?" ;
 var DATA="&username="+username+"&password="+password+"&code="+code;
 $.getJSON(URL+DATA,function(json){
 if(json.code=='code_error') {
 alert('Verification code error, please re-enter the verification code');
 }
 if(json.username=='true_u'&&json.password=='true_p'){
 //alert(json.username+"| "+username+'...1');
 window.location="index.php";
 }
 if(json.username=='error_u'||json.password=='error_p'){
 alert( "The username or password entered is incorrect, please check and log in again!");
 window.location="login.php";
 }
 });
 });

Backend checkLogin.php key code:

$code=$_GET['code'];
 if($code!=$_SESSION['captchaCode']['content'])
 {$adminInfo['code']='code_error' ;};

 if($row['username']==$username&&$row['password']==$password){

 $_SESSION['username']=$row['username'];
 $adminInfo['username']='true_u';
 $adminInfo['password']='true_p';
 mysql_close();
 }else
 if($row['username']!=$username){
 $adminInfo['username']='error_u';
 }
 if($row['password']!=$password){
 $adminInfo['password']='error_p';
 }

 //var_dump ($adminInfo);exit;
 echo json_encode($adminInfo);

The details are as follows: checkCode.class.php//Verification code

/*
* Captcha Class base on PHP GD Lib
* @author Design
* @version 1.0
* @copyright js8.in 2010 bbs.it-home.org
* @demo
* include('captchaClass.php');
* $captchaDemo=new Captcha();
* $captchaDemo->createImage();
*/
class Captcha{
 //@Define the height of the verification code image
 private $height;
 //@Define the width of the verification code image
 private $width;
 //@Define the number of verification code characters
 private $textNum;
 //@Define the content of the verification code characters
 private $textContent;
 //@ Define character color
 private $fontColor;
 //@Define random text color
 private $randFontColor;
 //@Define font size
 private $fontSize;
 //@Define font
 private $fontFamily;
 //@ Define the background color
 private $bgColor;
 //@Define the random background color
 private $randBgColor;
 //@Define the character language
 private $textLang;
 //@Define the number of interference points
 private $noisePoint;
 / /@Define the number of interference lines
 private $noiseLine;
 //@Define whether to distort
 private $distortion;
 //@Define the distorted image source
 private $distortionImage;
 //@Define whether there is a border
 private $showBorder;
 //@Define verification code image source
 private $image;

 //@Constructor constructor
 public function Captcha(){
 $this->textNum=4;
 $this->fontSize=16;
 $ this->fontFamily='c:\windows\fontsSIMYOU.ttf';//Set the Chinese font, you can change it to the Linux directory
 $this->textLang='en';
 $this->noisePoint=30 ;
 $this->noiseLine=3;
 $this->distortion=false;
 $this->showBorder=false;
 }

 //@Set the image width
 public function setWidth($w){
 $this->width=$w;
 }

 //@Set the image height
 public function setHeight($h){
 $this->height=$h;
 }

 //@Set the character Number
 public function setTextNumber($textN){
 $this->textNum=$textN;
 }

 //@Set character color
 public function setFontColor($fc){
 $this->fontColor=sscanf ($fc,'#%2x%2x%2x');
 }

 //@Set the font size
 public function setFontSize($n){
 $this->fontSize=$n;
 }

 // @Set the font
 public function setFontFamily($ffUrl){
 $this->fontFamily=$ffUrl;
 }

 //@Set the character language
 public function setTextLang($lang){
 $this->textLang= $lang;
 }

 //@Set the picture background
 public function setBgColor($bc){
 $this->bgColor=sscanf($bc,'#%2x%2x%2x');
 }

 //@Set the number of interference points
 public function setNoisePoint($n){
 $this->noisePoint=$n;
 }

 //@Set the number of interference lines
 public function setNoiseLine($n){
 $this ->noiseLine=$n;
 }

 //@Set whether to display the border
 public function setDistortion($b){
 $this->distortion=$b;
 }

 //@Set whether to display the border
 public function setShowBorder($border){
 $this->showBorder=$border;
 }

 //@Initialization verification code picture
 public function initImage(){
 if(empty($this->width)) {$this->width=floor($this->fontSize*1.3)*$this->textNum+10;}
 if(empty($this->height)){$this->height =$this->fontSize*2;}
 $this->image=imagecreatetruecolor($this->width,$this->height);
 if(empty($this->bgColor)){
 $this->randBgColor=imagecolorallocate($this->image,mt_rand(100,255),mt_rand(100,255),mt_rand(100,255));
 }else{
 $this->randBgColor=imagecolorallocate($this- >image,$this->bgColor[0],$this->bgColor[1],$this->bgColor[2]);
 }
 imagefill($this->image,0,0 ,$this->randBgColor);
 }

 //@Generate random characters
 public function randText($type){
 $string='';
 switch($type){
 case 'en':
 $ str='ABCDEFGHJKLMNPQRSTUVWXY3456789';
 for($i=0;$i<$this->textNum;$i++){
 $string=$string.','.$str[mt_rand(0,29)];
 }
 break;
 case 'cn':
 for($i=0;$i<$this->textNum;$i++) {
 $string=$string.','.chr(rand(0xB0, 0xCC)).chr(rand(0xA1,0xBB));
 }
 $string=iconv('GB2312','UTF-8',$string); //Convert encoding to utf8
 break;
 }
 return substr ($string,1);
 }

 //@Output text to verification code
 public function createText(){
 $textArray=explode(',',$this->randText($this->textLang) );
 $this->textContent=join('',$textArray);
 if(empty($this->fontColor)){
 $this->randFontColor=imagecolorallocate($this->image, mt_rand(0,100),mt_rand(0,100),mt_rand(0,100));
 }else{
 $this->randFontColor=imagecolorallocate($this->image,$this->fontColor[0],$this- >fontColor[1],$this->fontColor[2]);
 }
 for($i=0;$i<$this->textNum;$i++){
 $angle=mt_rand(-1,1)*mt_rand(1,20);
 imagettftext($this->image,$this->fontSize,$angle,5+$i*floor($this->fontSize*1.3),floor($this->height*0.75),$this->randFontColor,$this->fontFamily,$textArray[$i]);
 }
 }

 //@生成干扰点
 public function createNoisePoint(){
 for($i=0;$i<$this->noisePoint;$i++){
 $pointColor=imagecolorallocate($this->image,mt_rand(0,255),mt_rand(0,255),mt_rand(0,255));
 imagesetpixel($this->image,mt_rand(0,$this->width),mt_rand(0,$this->height),$pointColor);
 }

 }

 //@产生干扰线
 public function createNoiseLine(){
 for($i=0;$i<$this->noiseLine;$i++) {
 $lineColor=imagecolorallocate($this->image,mt_rand(0,255),mt_rand(0,255),20);
 imageline($this->image,0,mt_rand(0,$this->width),$this->width,mt_rand(0,$this->height),$lineColor);
 }
 }

 //@扭曲文字
 public function distortionText(){
 $this->distortionImage=imagecreatetruecolor($this->width,$this->height);
 imagefill($this->distortionImage,0,0,$this->randBgColor);
 for($x=0;$x<$this->width;$x++){
 for($y=0;$y<$this->height;$y++){
 $rgbColor=imagecolorat($this->image,$x,$y);
 imagesetpixel($this->distortionImage,(int)($x+sin($y/$this->height*2*M_PI-M_PI*0.5)*3),$y,$rgbColor);
 }
 }
 $this->image=$this->distortionImage;
 }

 //@生成验证码图片
 public function createImage(){
 $this->initImage(); //创建基本图片
 $this->createText(); //输出验证码字符
 if($this->distortion){$this->distortionText();} //扭曲文字
 $this->createNoisePoint(); //产生干扰点
 $this->createNoiseLine(); //产生干扰线
 if($this->showBorder){imagerectangle($this->image,0,0,$this->width-1,$this->height-1,$this->randFontColor);} //添加边框
 imagepng($this->image);
 imagedestroy($this->image);
 if($this->distortion){imagedestroy($this->$distortionImage);}
 return $this->textContent;
 }
}
?>
code.php//new 一个对象，负责图片的创建以及验证码文本写入session
session_start();
header("Content-type:image/png");
include('checkCode.class.php');
$captcha5=new Captcha();

//@设置验证码宽度
//$captcha5->setWidth(200);

//@设置验证码高度
//$captcha5->setHeight(50);

//@设置字符个数
$captcha5->setTextNumber(4);

//@设置字符颜色
//$captcha5->setFontColor('#ffffff');

//@设置字号大小
//$captcha5->setFontSize(25);

//@设置字体
$captcha5->setFontFamily('c:\windows\fonts\comic.TTF');

//@设置语言
$captcha5->setTextLang('en');

//@设置背景颜色
//$captcha5->setBgColor('#000000');

//@设置干扰点数量
//$captcha5->setNoisePoint(600);

//@设置干扰线数量
//$captcha5->setNoiseLine(10);

//@设置是否扭曲
//$captcha5->setDistortion(true);

//@设置是否显示边框
$captcha5->setShowBorder(true);

//输出验证码
$code=$captcha5->createImage();
$_SESSION['captchaCode']['content']=$code;
//$_SESSION['captchaCode']['time']=microtime();
?>

login.php//登陆页面，调用生成的验证码图片

  验证码：

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