在.jpg上添加.png水印

I have line: imagejpeg($this->image, $file, $quality);

How can add on this image watermark.png?

Check this, http://php.net/manual/en/image.examples-watermark.php

1. Open the image (imagecreatefrompng)
2. Copy it onto the jpg (imagecopy or other copy functions)
3. Save the resulting jpg
4. ?????
5. PROFIT!