diff --git a/theme/image.php b/theme/image.php
index 9659b91ed01..58b564bafe4 100644
--- a/theme/image.php
+++ b/theme/image.php
@@ -68,6 +68,7 @@ if (file_exists("$CFG->dirroot/theme/$themename/config.php")) {
 }
 
 $candidatelocation = "$CFG->cachedir/theme/$themename/pix/$component";
+$etag = sha1("$themename/$component/$rev/$image");
 
 if ($rev > -1) {
     if (file_exists("$candidatelocation/$image.error")) {
@@ -96,15 +97,16 @@ if ($rev > -1) {
         if (!empty($_SERVER['HTTP_IF_NONE_MATCH']) || !empty($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
             // we do not actually need to verify the etag value because our files
             // never change in cache because we increment the rev parameter
-            $lifetime = 60*60*24*30; // 30 days
+            $lifetime = 60*60*24*60; // 60 days only - the revision may get incremented quite often
             $mimetype = get_contenttype_from_ext($ext);
             header('HTTP/1.1 304 Not Modified');
             header('Expires: '. gmdate('D, d M Y H:i:s', time() + $lifetime) .' GMT');
             header('Cache-Control: public, max-age='.$lifetime);
             header('Content-Type: '.$mimetype);
+            header('Etag: '.$etag);
             die;
         }
-        send_cached_image($cacheimage, $rev);
+        send_cached_image($cacheimage, $etag);
     }
 }
 
@@ -121,6 +123,7 @@ $theme = theme_config::load($themename);
 $imagefile = $theme->resolve_image_location($image, $component);
 
 $rev = theme_get_revision();
+$etag = sha1("$themename/$component/$rev/$image");
 
 if (empty($imagefile) or !is_readable($imagefile)) {
     if ($rev > -1) {
@@ -144,7 +147,7 @@ if ($rev > -1) {
         }
         copy($imagefile, $cacheimage);
     }
-    send_cached_image($cacheimage, $rev);
+    send_cached_image($cacheimage, $etag);
 
 } else {
     send_uncached_image($imagefile);
@@ -156,19 +159,19 @@ if ($rev > -1) {
 // we are not using filelib because we need to fine tune all header
 // parameters to get the best performance.
 
-function send_cached_image($imagepath, $rev) {
+function send_cached_image($imagepath, $etag) {
     global $CFG;
     require("$CFG->dirroot/lib/xsendfilelib.php");
 
-    $lifetime = 60*60*24*30; // 30 days
+    $lifetime = 60*60*24*60; // 60 days only - the revision may get incremented quite often
     $pathinfo = pathinfo($imagepath);
     $imagename = $pathinfo['filename'].'.'.$pathinfo['extension'];
 
     $mimetype = get_contenttype_from_ext($pathinfo['extension']);
 
-    header('Etag: '.md5("$rev/$imagepath"));
+    header('Etag: '.$etag);
     header('Content-Disposition: inline; filename="'.$imagename.'"');
-    header('Last-Modified: '. gmdate('D, d M Y H:i:s', time()) .' GMT');
+    header('Last-Modified: '. gmdate('D, d M Y H:i:s', filemtime($imagepath)) .' GMT');
     header('Expires: '. gmdate('D, d M Y H:i:s', time() + $lifetime) .' GMT');
     header('Pragma: ');
     header('Cache-Control: public, max-age='.$lifetime);