PHP検証コード機能の実現

/**
	 *       
	 */
	public function actionVerfiycode() {
		Header ( "Content-type: image/gif" );
		$border = 0; //      1 :0  
		$how = 4; //     
		$w = $how * 15; //    
		$h = 20; //    
		$fontsize = 5; //    
		$alpha = "abcdefghijkmnopqrstuvwxyz"; //     1:  
		$number = "0123456789"; //     2:  
		$randcode = ""; //         
		srand ( ( double ) microtime () * 1000000 ); //        
		$im = ImageCreate ( $w, $h ); //      
		$bgcolor = ImageColorAllocate ( $im, 255, 255, 255 ); //      
		ImageFill ( $im, 0, 0, $bgcolor ); //     
		if ($border) {
			$black = ImageColorAllocate ( $im, 0, 0, 0 ); //      
			ImageRectangle ( $im, 0, 0, $w - 1, $h - 1, $black ); //    
		}
		for($i = 0; $i < $how; $i ++) {
			$alpha_or_number = mt_rand ( 0, 1 ); //      
			$str = $alpha_or_number ? $alpha : $number;
			$which = mt_rand ( 0, strlen ( $str ) - 1 ); //     
			$code = substr ( $str, $which, 1 ); //   
			$j = ! $i ? 4 : $j + 15; //     
			$color3 = ImageColorAllocate ( $im, mt_rand ( 0, 100 ), mt_rand ( 0, 100 ), mt_rand ( 0, 100 ) ); //      
			ImageChar ( $im, $fontsize, $j, 3, $code, $color3 ); //   
			$randcode .= $code; //          
		}
		
		for($i = 0; $i < 5; $i ++) //      
		{
			$color1 = ImageColorAllocate ( $im, mt_rand ( 0, 255 ), mt_rand ( 0, 255 ), mt_rand ( 0, 255 ) ); //     
			ImageArc ( $im, mt_rand ( - 5, $w ), mt_rand ( - 5, $h ), mt_rand ( 20, 300 ), mt_rand ( 20, 200 ), 55, 44, $color1 ); //   
		}
		for($i = 0; $i < $how * 40; $i ++) //      
		{
			$color2 = ImageColorAllocate ( $im, mt_rand ( 0, 255 ), mt_rand ( 0, 255 ), mt_rand ( 0, 255 ) ); //      
			ImageSetPixel ( $im, mt_rand ( 0, $w ), mt_rand ( 0, $h ), $color2 ); //   
		}
		$session=new CHttpSession;
		$session->open();	
		Yii::app()->session->add('randcode',$randcode);
		/*    */
		Imagegif ( $im );
		ImageDestroy ( $im );
		/*    */
	
	}