upload picture and make it my css background-image
You can do something like this:

hook_node_view($node, $viewmode, $langcode)
{
  if(count($node-&gt;field_background_image) &amp;&amp; isset($node-&gt;field_backround_image[LANGUAGE_NONE][0]['uri']))
  {
    $node-&gt;content['#attached']['css'][] = array
    (
      'type' =&gt; 'inline',
      'data' =&gt; '#some_div{background-image:url(' . file_create_url($node-&gt;field_background_image[LANGUAGE_NONE][0]['uri']) . ');}',
    );
  }
}