function getPictures($album_id, $element_per_page, $piwigo_API, $piwigo_user_login, $piwigo_user_pwd)
{
  $res = null;
  
  //Login
  $loginData = http_build_query(
    array(
      'method' => 'pwg.session.login',
      'username' => $piwigo_user_login,
      'password' => $piwigo_user_pwd
    )
  );
  
  $loginOpts = array('http' =>
    array(
      'method' => 'POST',
      'header' => 'Content-Type: application/x-www-form-urlencoded',
      'content' => $loginData
    )
  );

  $loginContext = stream_context_create($loginOpts);
  $login = file_get_contents($piwigo_API . '?format=json', false, $loginContext);
  
  //Get session id in cookie
  $loginID = '';
  $cookies = array();
  foreach ($http_response_header as $hdr)
  {
    if (preg_match('/Set-Cookie:\s*pwg_id=([\w]+);/', $hdr, $matches))
    {
      array_push($cookies, $matches[1]);
    }
  }
  $loginID = $cookies[0];
  
  //Get pictures
  $responseOpts = array('http' =>
    array(
      'method' => 'GET',
      'header' => 'Cookie: pwg_id=' . $loginID
    )
  );

  $responseContext = stream_context_create($responseOpts);
  $response = file_get_contents($piwigo_API . '?format=json&method=pwg.categories.getImages&order=name&cat_id=' . $album_id . '&per_page=' . $element_per_page, false, $responseContext);
  $res = json_decode($response);
  
  //Logout
  $logoutOpts = array('http' =>
    array(
      'method' => 'GET',
      'header' => 'Cookie: pwg_id=' . $loginID
    )
  );

  $logoutContext = stream_context_create($logoutOpts);
  $logout = file_get_contents($piwigo_API . '?format=json&method=pwg.session.logout', false, $logoutContext);
  
  return $res;
}