Drupal: Display an image from a node in a form.

show_preview_image.php

<?php

$node = node_load(NID_HERE);


if ($node->field_image[LANGUAGE_NONE][0]['fid']) {
  $file = file_load($node->field_image[LANGUAGE_NONE][0]['fid']);

  $form['image_preview'] = array(
    '#markup' => theme('image', array('uri' => $file->uri));
  );

}