How to get the Object based on File ID (FID)
You can use an EntityFieldQuery, e.g.

$field_name = 'field_something';
$fid = 123;

$query = new \EntityFieldQuery();
$query-&gt;entityCondition('node')
  -&gt;propertyCondition('type', 'the_type')
  -&gt;fieldCondition($field_name, 'fid', $fid);

$results = $query-&gt;execute();
if (!empty($results['node'])) {
  $nodes = node_load_multiple(array_keys($results['node']));

  // $nodes contains all nodes that reference the given file via field_something.
}