$znak_hw = getimagesize("znak.png");
$foto_hw = getimagesize("foto.jpg");

$znak = imagecreatefrompng ("znak.png");
$foto = imagecreatefromjpeg ("foto.jpg");

imagecopy ($foto,
$znak,
$foto_hw[0] - $znak_hw[0],
$foto_hw[1] - $znak_hw[1],
0,
0,
$znak_hw[0],
$znak_hw[1]);

imagejpeg ($foto, "done.jpg", "100");

imagedestroy ($znak);
imagedestroy ($foto);