php-淘宝API图片上传问题

$c = new TopClient;
$c->appkey = "1*****2";
$c->secretKey ="b***************9";
$req = new PictureUploadRequest;
$req->setPictureCategoryId("0");

$content = file_get_contents("http://img20.360buyimg.com/vc/jfs/t1936/10/62548506/219327/ba45f44c/55ebc1baNdb5f788d.jpg");

//=========这里的setImg应该怎么传网络上的图片呢？====

$req->setImg($content);

$req->setImageInputTitle("Bule.jpg");
$req->setTitle("图片名称");
$req->setClientType("client:computer");
$resp = $c->execute($req,"********************");
var_dump($resp);

新手问题，要把网络图片上传到图片空间，php的代码应该怎么编写？