Domain Access - imagestyles per Domain

gistfile1.php

<?php
/** 
 * Helper function to get current machine_name of domain.
 * - used in preprocess functions for setting corresponding image-styles for fields
 * @return string 
 *   machine_name of current domain
 */
function my_module_get_domain_machine_name() {
  $machine_name = '';
  // Get machine_name for actual domain.
  $domain = domain_get_domain();
  if (!empty($domain) && !$domain['is_default']) {
    $machine_name = $domain['machine_name'];
  }
  return $machine_name;
}

gistfile2.php

<?php
/**
 * Implements hook_preprocess_node().
 */
function my_module_preprocess_node(&$vars) {
  // Check for node-type we want to preprocess.
  if ($vars['type'] == '{my_content_type}') {
    // Get machine name for domain.
    $domain_name = my_module_get_domain_machine_name();
    // Lookup field with image-style and add domain-name to style name.
    if (!empty($vars['content']['field_image'])) {
      $current_style = $vars['content']['field_image'][0]['#image_style'];
      $variables['content']['field_image'][0]['#image_style'] = implode('_', array($current_style, $domain_name));
    }
  }
}