$image = drupal_http_request($link);

  $path_array = explode('/', $link);
  $filename = end($path_array);
  
  $save_to = file_directory_path().'/_images/'.$filename;
  $temp = '/opt/httpd/htdocs/devphp.caribbeantravelmag.com/files/blog/'.$filename;
  
  file_put_contents($temp, file_get_contents($link));

http://stackoverflow.com/questions/724391/save-image-from-php-url-using-php

Fetching and storing remote image

drupal

PHP