First workable version:maybe need more test.

image_url_formatter.info

 name = Image URL Formatter
+description = "Add an URL formatter for image field"
+core = 7.x
+dependencies[] = field
+dependencies[] = image
+files[] = image_url_formatter.module
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image_url_formatter.module

+<?php
+
+/**
+ * @file
+ * Add an URL formatter for image field
+ */
+ 
+/**
+ * Implements hook_theme().
+ */
+function image_url_formatter_theme() {
+  return array(
+    'image_url_formatter' => array(
+      'variables' => array(
+        'item' => NULL, 
+				'path' => NULL, 
+				'image_style' => NULL,
+      ),
+    ),
+  );
+}
+ 
+/**
+ * Implements hook_field_formatter_info().
+ */
+function image_url_formatter_field_formatter_info() {
+  $formatters = array(
+    'image_url' => array(
+      'label' => t('Image URL'),
+      'field types' => array('image'),
+      'settings' => array('image_style' => '', 'image_link' => ''),
+    ),
+  );
+
+  return $formatters;
+}
+
+/**
+ * Implements hook_field_formatter_settings_form().
+ */
+function image_url_formatter_field_formatter_settings_form($field, $instance, $view_mode, $form, &$form_state) {
+  $display = $instance['display'][$view_mode];
+  $settings = $display['settings'];
+
+  $image_styles = image_style_options(FALSE);
+  $element['image_style'] = array(
+    '#title' => t('Image style'),
+    '#type' => 'select',
+    '#default_value' => $settings['image_style'],
+    '#empty_option' => t('None (original image)'),
+    '#options' => $image_styles,
+  );
+
+  $link_types = array(
+    'content' => t('Content'),
+    'file' => t('File'),
+  );
+  $element['image_link'] = array(
+    '#title' => t('Link image url to'),
+    '#type' => 'select',
+    '#default_value' => $settings['image_link'],
+    '#empty_option' => t('Nothing'),
+    '#options' => $link_types,
+  );
+
+  return $element;
+}
+
+/**
+ * Implements hook_field_formatter_settings_summary().
+ */
+function image_url_formatter_field_formatter_settings_summary($field, $instance, $view_mode) {
+  $display = $instance['display'][$view_mode];
+  $settings = $display['settings'];
+
+  $summary = array();
+
+  $image_styles = image_style_options(FALSE);
+  // Unset possible 'No defined styles' option.
+  unset($image_styles['']);
+  // Styles could be lost because of enabled/disabled modules that defines
+  // their styles in code.
+  if (isset($image_styles[$settings['image_style']])) {
+    $summary[] = t('URL for image style: @style', array('@style' => $image_styles[$settings['image_style']]));
+  }
+  else {
+    $summary[] = t('Original image URL');
+  }
+
+  $link_types = array(
+    'content' => t('Linked to content'),
+    'file' => t('Linked to file'),
+  );
+  // Display this setting only if image is linked.
+  if (isset($link_types[$settings['image_link']])) {
+    $summary[] = $link_types[$settings['image_link']];
+  }
+
+  return implode('<br />', $summary);
+}
+/**
+ * Implements hook_field_formatter_view().
+ */
+function image_url_formatter_field_formatter_view($entity_type, $entity, $field, $instance, $langcode, $items, $display) {
+  $element = array();
+	
+  switch ($display['type']) {
+    case 'image_url':
+		  // Check if the formatter involves a link.
+      if ($display['settings']['image_link'] == 'content') {
+        $uri = entity_uri($entity_type, $entity);
+      }
+      elseif ($display['settings']['image_link'] == 'file') {
+        $link_file = TRUE;
+      }
+
+      foreach ($items as $delta => $item) {
+        if (isset($link_file)) {
+          $uri = array(
+            'path' => file_create_url($item['uri']),
+            'options' => array(),
+          );
+        }
+				//debug($item);
+        $element[$delta] = array(
+          '#theme' => 'image_url_formatter',
+          '#item' => $item,
+          '#image_style' => $display['settings']['image_style'],
+          '#path' => isset($uri) ? $uri : '',
+        );
+      }
+
+      break;
+
+  }
+
+  return $element;
+}
+
+/**
+ * Returns HTML for an image url field formatter.
+ *
+ * @param $variables
+ *   An associative array containing:
+ *   - item: An array of image data.
+ *   - image_style: An optional image style.
+ *   - path: An array containing the link 'path' and link 'options'.
+ *
+ * @ingroup themeable
+ */
+function theme_image_url_formatter($variables) {
+  $item = $variables['item'];
+  $image = array(
+    'path' => $item['uri'],
+    'alt' => $item['alt'],
+  );
+  // Do not output an empty 'title' attribute.
+  if (drupal_strlen($item['title']) > 0) {
+    $image['title'] = $item['title'];
+  }
+  $output = file_create_url($item['uri']);
+  if ($variables['image_style']) {
+	  //debug($image);
+    $image['style_name'] = $variables['image_style'];
+		$output = image_style_url($image['style_name'], $item['uri']);
+  }
+  if ($variables['path']) {
+    $path = $variables['path']['path'];
+    $options = $variables['path']['options'];
+    // When displaying an image inside a link, the html option must be TRUE.
+    $options['html'] = TRUE;
+    $output = l($output, $path, $options);
+  }
+
+  return $output;
+}
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