--- imagecache.module 
+++ imagecache.module 
@@ -46,10 +46,10 @@
  */
 define('IMAGECACHE_STORAGE_OVERRIDE', 2);
 
+/**
+ * Define maximum number of subdomain (if enabled) to split image.
+ */
+define('IMAGECACHE_MAX_SUBDOMAIN', 3);
 
 /*********************************************************************************************
  * Drupal Hooks
@@ -323,7 +323,7 @@
   $args = array('absolute' => TRUE, 'query' => empty($bypass_browser_cache) ? NULL : time());
   switch (variable_get('file_downloads', FILE_DOWNLOADS_PUBLIC)) {
     case FILE_DOWNLOADS_PUBLIC:
-      return url($GLOBALS['base_url'] . '/' . file_directory_path() .'/imagecache/'. $presetname .'/'. $path, $args);
+      return url(_imagecache_get_subdomain($filepath) . '/' . file_directory_path() .'/imagecache/'. $presetname .'/'. $path, $args);
     case FILE_DOWNLOADS_PRIVATE:
       return url('system/files/imagecache/'. $presetname .'/'. $path, $args);
   }
@@ -1109,3 +1109,43 @@
   imagecache_presets(TRUE);
 }
 
+/** Return domain to add to image path.
+ *
+ * Generate domain to add to image to generate complete URL.
+ * This function use first letter of name to redirect the same image into
+ * the same domain everytime.
+ *
+ * @param $file_name
+ *   Path and name of image.
+ *
+ * @return
+ *   Domain do add into image absolute path.
+ */
+function _imagecache_get_subdomain($file_name = NULL) {
+  // Return empty if subdomain is not enabled
+  if(!variable_get('imagecache_subdomain_enable_global', FALSE) || is_null($file_name)) {
+    return $GLOBALS['base_url'];
+  }
+
+  // Extract config
+  $config = variable_get('imagecache_subdomain_config', array());
+
+  // Count number of subdomain
+  $num_subdomain = count($config);
+
+  // Extract first char of filename
+  // TODO: use regexp to extract only alphanumeric char
+  $first_char = substr(basename($file_name), 0, 1);
+
+  // Define list of possible first char value and generate array
+  // TODO: it's possible improve performance using a defined array (no generation to runtime)
+  $char_list = 'aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTuUvVwWxXyYzZ0123456789-_.+';
+  $char_key  = array_flip(str_split($char_list));
+
+  // Find subdomain to use
+  $subdomain = floor(($num_subdomain + 1) * $char_key[$first_char] / strlen($char_list));
+
+  // Return correct subdomain
+  return $config[$subdomain]['uri'];
+}
+