Upload Nodes with Image Fields
There is a problem in Drupal core. I made an issue for it here and a patch has been supplied, but it didn't work properly for me: https://www.drupal.org/node/1912458

I did get it to work by only doing part of what the patch does.

Find line 504 of modules/file/file.field.inc and change it from this:

if (($field['cardinality'] == FIELD_CARDINALITY_UNLIMITED || $delta &lt; $field['cardinality']) &amp;&amp; empty($form_state['programmed'])) {


To this:

if (($field['cardinality'] == FIELD_CARDINALITY_UNLIMITED || $delta &lt; $field['cardinality'])) {


I don't know if this produces adverse side effects anywhere else, but it does allow services to be used in the way you are using it.