private function createBg()
{
$this->image = imagecreate($this->width, $this->height);
$this->back = imagecolorallocate($this->image, mt_rand(200, 255), mt_rand(200, 255), mt_rand(200, 255));
imagefilledrectangle($this->image, 0, $this->height, $this->width, 0, $this->back);
}