Attaching image files to nodes programmatically in Drupal 7 – Stack Overflow.

$filepath = drupal_realpath('misc/druplicon.png');// Create managed File object and associate with Image field.
  $file =(object) array('uid'=>1,'uri'=> $filepath,'filemime'=> file_get_mimetype($filepath),'status'=>1,);// We save the file to the root of the files directory.
  $file = file_copy($file,'public://');

  $node->field_image[LANGUAGE_NONE][0]=(array)$file;`