diff --git a/image.php b/image.php
index cccda64b7..36da375aa 100644
--- a/image.php
+++ b/image.php
@@ -28,6 +28,8 @@
 
 		if (file_exists($filename)) {
 			header("Content-type: image/png");
+			$stamp = gmdate("D, d M Y H:i:s", filemtime($filename)). " GMT";
+			header("Last-Modified: $stamp", true);
 			echo file_get_contents($filename);
 		} else {
 			header($_SERVER["SERVER_PROTOCOL"]." 404 Not Found");