一个自己写的10以内的加减法验证码

<?php
/*图片验证码文件，加减计算方式*/

class ImageCode{
	
	private $Jiashu  = 0;        //加数或者减数
	private $JianShu = 0;        //被加数或者被减数
	private $YunSuan = '';       //运算符
	private $DeShu   = 0;        //得数
	private $String  = '';       //字符串样式
	private $Img;                //图片对象
	private $Width   = 100;      //图片宽度
	private $Height  = 50;       //图片高度
	private $Ttf     = 'Num.ttf';//字体文件
	private $Session = 'code';   //Session变量
	
	
	
	private function JiaShu(){
		header('Content-type:image/png');
		$this -> Jiashu  = rand(1, 10);
		$this -> JianShu = rand(1, 10);
		$this -> YunSuan= $this -> Jiashu > $this -> JianShu ? '-' : '+';
		$this -> DeShu   = $this -> Jiashu > $this -> JianShu ? $this -> Jiashu - $this -> JianShu : $this -> Jiashu + $this -> JianShu;
	}
	
	public function Show( $W = 100, $H = 50, $T = 'Num.ttf', $Code = 'code' ){
		$this -> JiaShu();
		$this -> String = $this -> Jiashu . $this -> YunSuan . $this -> JianShu . '= ? ';
		$this -> Width  = $W;
		$this -> Height = $H;
		$this -> Ttf    = $T;
		$this -> Session= $Code;
		session_start();
		$_SESSION[$this -> Session] = $this -> DeShu;
		$this -> Images();
	}
	
	private function Images(){
		$this -> Img = imagecreate($this -> Width, $this -> Height);
		$background_color = imagecolorallocate ($this -> Img, 255, 255, 255);
		imagecolortransparent($this -> Img, $background_color);
        imagettftext($this -> Img, 14, 0, 1, 20, imagecolorallocate ($this -> Img, 0, 0, 0), $this -> Ttf, $this -> String );
		$this -> EchoImages();
	}
	
	private function EchoImages(){
		imagepng($this -> Img);
		imagedestroy($this -> Img);
	}
	
}

$ImageCode = new ImageCode;
$ImageCode -> Show(130, 35, 'Num.ttf', 'code');