将文件从URL放入POST请求

Question

I am using PHP script for files uploading to image hosting. Necessary files not stored on disk and available via http URL. So, my first step is to download image to disk:

file_put_contents('sample.jpg', file_get_contents($url));

And then attach it to curl request:

curl_setopt($ch, CURLOPT_POSTFIELDS,      array(
  'image' => '@' . realpath('sample.jpg'),
  'title' => 'sample.jpg'
  ));

Am I able to do the same without file downloading: specify URL in parameters for curl to automatically take data from URL?