You should be able to use file_get_contents for this one. In order to use an URL with file_get_contents make sure allow_url_fopen is enabled in you php.ini file.

define('DIRECTORY', '/home/user/uploads');

$content = file_get_contents('http://anothersite/images/goods.jpg');
file_put_contents(DIRECTORY . '/image.jpg', $content);
Make sure that you have write permission to the directory where you want to store the image; to make the folder writable you could do this:

chmod +w /home/users/uploads