Implementing user registration and login function based on PHP

<?php
/**
* Captcha class
*/
class Captcha
{
   
  function __construct()
  {
    # code...
  }
}

<?php
/**
* Captcha class
*/
class Captcha
{
  private $codeNum;  //验证码位数
  private $width;  //验证码图片宽度
  private $height;  //验证码图片高度
  private $img;  //图像资源句柄
  private $lineFlag;  //是否生成干扰线条
  private $piexFlag;  //是否生成干扰点
  private $fontSize;  //字体大小
  private $code;  //验证码字符
  private $string;  //生成验证码的字符集
  private $font;  //字体
  function __construct($codeNum = 4,$height = 50,$width = 150,$fontSize = 20,$lineFlag = true,$piexFlag = true)
  {
    $this->string = &#39;qwertyupmkjnhbgvfcdsxa123456789&#39;;  //去除一些相近的字符
    $this->codeNum = $codeNum;
    $this->height = $height;
    $this->width = $width;
    $this->lineFlag = $lineFlag;
    $this->piexFlag = $piexFlag;
    $this->font = dirname(__FILE__).&#39;/fonts/consola.ttf&#39;;
    $this->fontSize = $fontSize;
  }
}

//创建图像资源 
public function createImage(){
    $this->img = imagecreate($this->width, $this->height);  //创建图像资源
    imagecolorallocate($this->img,mt_rand(0,100),mt_rand(0,100),mt_rand(0,100));  //填充图像背景（使用浅色）
  }

//创建干扰线条（默认四条）
public function createLines(){
    for ($i=0; $i < 4; $i++) {
      $color = imagecolorallocate($this->img,mt_rand(0,155),mt_rand(0,155),mt_rand(0,155));  //使用浅色
      imageline($this->img,mt_rand(0,$this->width),mt_rand(0,$this->height),mt_rand(0,$this->width),mt_rand(0,$this->height),$color);
    }
  }

//创建干扰点 （默认一百个点）
public function createPiex(){
    for ($i=0; $i < 100; $i++) {
      $color = imagecolorallocate($this->img,mt_rand(0,255),mt_rand(0,255),mt_rand(0,255));
      imagesetpixel($this->img,mt_rand(0,$this->width),mt_rand(0,$this->height),$color);
    }
  }

public function show()
 {
   $this->createImage();
   $this->createCode();
   if ($this->lineFlag) {  //是否创建干扰线条
     $this->createLines();
   }
   if ($this->piexFlag) {  //是否创建干扰点
     $this->createPiex();
   }
   header('Content-type:image/png');  //请求页面的内容是png格式的图像
   imagepng($this->img);  //以png格式输出图像
   imagedestroy($this->img);  //清除图像资源，释放内存
 }

public function getCode(){
    return $this->code;
  }

string = 'qwertyupmkjnhbgvfcdsxa123456789';
    $this->codeNum = $codeNum;
    $this->height = $height;
    $this->width = $width;
    $this->lineFlag = $lineFlag;
    $this->piexFlag = $piexFlag;
    $this->font = dirname(__FILE__).'/fonts/consola.ttf';
    $this->fontSize = $fontSize;
  }
 
  public function createImage(){
    $this->img = imagecreate($this->width, $this->height);
    imagecolorallocate($this->img,mt_rand(0,100),mt_rand(0,100),mt_rand(0,100));
  }
 
  public function createCode(){
    $strlen = strlen($this->string)-1;
    for ($i=0; $i < $this->codeNum; $i++) {
      $this->code .= $this->string[mt_rand(0,$strlen)];
    }
    $_SESSION['code'] = $this->code;
    $diff = $this->width/$this->codeNum;
    for ($i=0; $i < $this->codeNum; $i++) {
      $txtColor = imagecolorallocate($this->img,mt_rand(100,255),mt_rand(100,255),mt_rand(100,255));
      imagettftext($this->img, $this->fontSize, mt_rand(-30,30), $diff*$i+mt_rand(3,8), mt_rand(20,$this->height-10), $txtColor, $this->font, $this->code[$i]);
    }
  }
 
  public function createLines(){
    for ($i=0; $i < 4; $i++) {
      $color = imagecolorallocate($this->img,mt_rand(0,155),mt_rand(0,155),mt_rand(0,155));
      imageline($this->img,mt_rand(0,$this->width),mt_rand(0,$this->height),mt_rand(0,$this->width),mt_rand(0,$this->height),$color);
    }
  }
 
  public function createPiexs(){
    for ($i=0; $i < 100; $i++) {
      $color = imagecolorallocate($this->img,mt_rand(0,255),mt_rand(0,255),mt_rand(0,255));
      imagesetpixel($this->img,mt_rand(0,$this->width),mt_rand(0,$this->height),$color);
    }
  }
 
  public function show()
  {
    $this->createImage();
    $this->createCode();
    if ($this->lineFlag) {
      $this->createLines();
    }
    if ($this->piexFlag) {
      $this->createPiexs();
    }
    header('Content-type:image/png');
    imagepng($this->img);
    imagedestroy($this->img);
  }
 
  public function getCode(){
    return $this->code;
  }
}

session_start(); //开启session
$captcha = new Captcha();  //实例化验证码类(可自定义参数)
$captcha->show();  //调用输出

<div class="form-group">
 <div class="col-sm-12">
   <img src="/static/imghw/default1.png"  data-src="admin/Captcha.php"  class="lazy"   alt="" id="codeimg" onclick="javascript:this.src = &#39;admin/Captcha.php?&#39;+Math.random();">
   <span>Click to Switch</span>
 </div>
</div>