diff --git imagecache/imagecache.module imagecache/imagecache.module
index 55d48ce..98b04ae 100644
--- imagecache/imagecache.module
+++ imagecache/imagecache.module
@@ -342,7 +342,7 @@ function imagecache_action_definition($action) {
  */
 function imagecache_create_url($presetname, $filepath, $bypass_browser_cache = FALSE, $absolute = TRUE) {
   $args = array(
-    'query' => empty($bypass_browser_cache) ? NULL : time(),
+    'query' => empty($bypass_browser_cache) ? filemtime($filepath) : time(),
     // Little hack to avoid having language_url_rewrite() prefix the path with the
     // language code, but preserve the domain rewriting.
     'language' => (object) array('language' => '', 'domain' => $GLOBALS['language']->domain),