Making watermark by merge image

function generateMyImage($img, $sig, $target) {
    $info = getimagesize($img);
    $mime = $info['mime'];
    $type = substr(strrchr($mime, '/'), 1);
    $image_types = array('jpeg', 'png', 'gif', 'bmp');
    if (!in_array($type, $image_types)) $type= 'Jpeg';
    $img_create_func = 'ImageCreateFrom' . $type;
    
    $dest = $img_create_func($img);
    $src = imagecreatefromjpeg($sig);
    $playW = imagesx($src);
    $playH = imagesy($src);

    $dH = $info[1] - $playH;
    imagecopymerge($dest, $src, 0, $dH, 0, 0, $playW, $playH, 100);
    imagegif($dest, $target);
    imagedestroy($dest);
    imagedestroy($src);
}