I just wanted to put the custom code that I used to migrate from the noderef/noderef image helper modules in drupal 6 to Image fields in drupal 7.

I had two types of images showing in drupal 6 - direct image fields which had a specific imagecache preset, and v via nodereference which had a different preset.

Then in drupal 7 I ran the content_migrate stuff for the imagefields and on the content types, added a list field (called image style where the options were named to be the same as available image styles tht I wanted to allow users to choose from) to each content type where the old image references were.

Following this, I ran this code:

/**
 * Implementation of hook_menu().
 */

function mymodule_menu() {
  $items['imagefix'] = array(
    'access callback' => TRUE,
    'page callback' => 'mymodule_imagefix',
    'type' => MENU_CALLBACK,
  );
  return $items;
  
}

/**
 * Fix Images on the upgraded site.
 */
 
function mymodule_imagefix() {
    // Complete style info for already imported images
 
  $entities = db_select('field_data_field_image', 'f')
    ->fields('f', array('entity_type', 'bundle', 'deleted', 'entity_id', 'revision_id', 'language', 'delta'))
    ->execute();
  
  foreach ($entities as $entity) {
  
        db_insert('field_data_field_image_style')
        ->fields(array(
          'entity_type' => $entity->entity_type,
          'bundle' => $entity->bundle,
          'deleted' => $entity->deleted,
          'entity_id' => $entity->entity_id,
          'revision_id' => $entity->revision_id,
          'language' => $entity->language,
          'delta' => $entity->delta,
          'field_image_style_value' => 'large',
        ))
      ->execute();
  
  }

  
  $revisions = db_select('field_revision_field_image', 'f')
    ->fields('f', array('entity_type', 'bundle', 'deleted', 'entity_id', 'revision_id', 'language', 'delta'))
    ->execute();
  
  foreach ($revisions as $revision) {
        db_insert('field_revision_field_image_style')
        ->fields(array(
          'entity_type' => $revision->entity_type,
          'bundle' => $revision->bundle,
          'deleted' => $revision->deleted,
          'entity_id' => $revision->entity_id,
          'revision_id' => $revision->revision_id,
          'language' => $revision->language,
          'delta' => $revision->delta,
          'field_image_style_value' => 'large',
        ))
      ->execute();
  
  }
  
    // 4. Migrate the relevant image data.
  $result = db_query("SELECT vid, nid, field_attached_image_nid FROM {content_field_attached_image} WHERE field_attached_image_nid <> '' ORDER BY nid ASC, vid ASC");
  $count=0;
  foreach ($result as $record) {
    // Select current data
    $image = db_query("SELECT deleted, MAX(revision_id), language, delta, field_image_fid, field_image_title, field_image_alt, field_image_title, field_image_width, field_image_height FROM {field_data_field_image} WHERE (entity_type = :entity and entity_id = :entity_id)", array(':entity' => 'node', ':entity_id' => $record->field_attached_image_nid))->fetchObject();
    
    $bundle = db_query("Select DISTINCT(type) from {node} where nid = :nid", array(':nid' => $record->nid, ))->fetchField();

    drupal_set_message(print_r($image, 1));
    drupal_set_message(print_r($bundle . ', ' . $record->nid . '' . $record->vid, 1));
    
    if (!is_null($image->field_image_fid)) {
    
      //Insert Image data
      db_insert('field_revision_field_image')
        ->fields(array(
          'entity_type' => 'node',
          'bundle' => $bundle,
          'deleted' => $image->deleted,
          'entity_id' => $record->nid,
          'revision_id' => $record->vid,
          'language' => $image->language,
          'delta' => $image->delta,
          'field_image_fid' => $image->field_image_fid,
          'field_image_alt' => $image->field_image_alt,
          'field_image_title' => $image->field_image_title,
          'field_image_title' => $image->field_image_width,
          'field_image_title' => $image->field_image_height
        ))
      ->execute();
      
      db_merge('field_data_field_image')
        ->key(array('entity_type' => 'node', 'entity_id' => $record->nid))
        ->fields(array(
          'entity_type' => 'node',
          'bundle' => $bundle,
          'deleted' => $image->deleted,
          'entity_id' => $record->nid,
          'revision_id' => $record->vid,
          'language' => $image->language,
          'delta' => $image->delta,
          'field_image_fid' => $image->field_image_fid,
          'field_image_alt' => $image->field_image_alt,
          'field_image_title' => $image->field_image_title,
          'field_image_title' => $image->field_image_width,
          'field_image_title' => $image->field_image_height
        ))
      ->execute();
      
      // Insert list field data.
      db_insert('field_revision_field_image_style')
        ->fields(array(
          'entity_type' => 'node',
          'bundle' => $bundle,
          'deleted' => $image->deleted,
          'entity_id' => $record->nid,
          'revision_id' => $record->vid,
          'language' => $image->language,
          'delta' => $image->delta,
          'field_image_style_value' => 'medium',
        ))
      ->execute();
      
      db_merge('field_data_field_image_style')
        ->key(array('entity_type' => 'node', 'entity_id' => $record->nid))
        ->fields(array(
          'entity_type' => 'node',
          'bundle' => $bundle,
          'deleted' => $image->deleted,
          'entity_id' => $record->nid,
          'revision_id' => $record->vid,
          'language' => $image->language,
          'delta' => $image->delta,
          'field_image_style_value' => 'medium',
        ))
      ->execute();
      $count++;
    }
  }
  drupal_set_message($count);

}

Code for changing the image style to what is set in the image_style field is here: http://drupal.org/node/1363250