diff --git a/core/includes/file.inc b/core/includes/file.inc
index b476bc7..47b028e 100644
--- a/core/includes/file.inc
+++ b/core/includes/file.inc
@@ -2046,7 +2046,9 @@ function file_download() {
       $function = $module . '_file_download';
       $result = $function($uri);
       if ($result == -1) {
-        return drupal_access_denied();
+        // Throw away the headers received so far.
+        $headers = array();
+        break;
       }
       if (isset($result) && is_array($result)) {
         $headers = array_merge($headers, $result);
@@ -2055,9 +2057,12 @@ function file_download() {
     if (count($headers)) {
       file_transfer($uri, $headers);
     }
-    return drupal_access_denied();
+    drupal_access_denied();
   }
-  return drupal_not_found();
+  else {
+    drupal_not_found();
+  }
+  drupal_exit();
 }
 
 
diff --git a/core/modules/image/image.module b/core/modules/image/image.module
index 8fd8cee..d19b01e 100644
--- a/core/modules/image/image.module
+++ b/core/modules/image/image.module
@@ -281,12 +281,9 @@ function image_file_download($uri) {
           // Send headers describing the image's size, and MIME-type...
           'Content-Type' => $info['mime_type'],
           'Content-Length' => $info['file_size'],
-          // ...and allow the file to be cached for two weeks (matching the
-          // value we/ use for the mod_expires settings in .htaccess) and
-          // ensure that caching proxies do not share the image with other
-          // users.
-          'Expires' => gmdate(DATE_RFC1123, REQUEST_TIME + 1209600),
-          'Cache-Control' => 'max-age=1209600, private, must-revalidate',
+          // By not explicitly setting them here, this uses normal Drupal
+          // Expires, Cache-Control and ETag headers to prevent proxy or
+          // browser caching of private images.
         );
       }
     }
diff --git a/core/modules/image/image.test b/core/modules/image/image.test
index ff783be..aa8b9ce 100644
--- a/core/modules/image/image.test
+++ b/core/modules/image/image.test
@@ -224,7 +224,22 @@ class ImageStylesPathAndUrlUnitTest extends DrupalWebTestCase {
     $this->assertEqual($this->drupalGetHeader('Content-Type'), $generated_image_info['mime_type'], t('Expected Content-Type was reported.'));
     $this->assertEqual($this->drupalGetHeader('Content-Length'), $generated_image_info['file_size'], t('Expected Content-Length was reported.'));
     if ($scheme == 'private') {
+      $this->assertEqual($this->drupalGetHeader('Expires'), 'Sun, 19 Nov 1978 05:00:00 GMT', t('Expires header was sent.'));
+      $this->assertEqual($this->drupalGetHeader('Cache-Control'), 'no-cache, must-revalidate, post-check=0, pre-check=0', t('Cache-Control header was set to prevent caching.'));
       $this->assertEqual($this->drupalGetHeader('X-Image-Owned-By'), 'image_module_test', t('Expected custom header has been added.'));
+      // Verify access is denied to private image styles.
+      $this->drupalLogout();
+      $this->drupalGet($generate_url);
+      $this->assertResponse(403, t('Confirmed that access is denied for the private image style.') );
+      // Verify that images are not appended to the response. Currently this test only uses PNG images.
+      if (strpos($generate_url, '.png') === FALSE ) {
+        $this->fail( t('Confirming that private image styles are not appended require PNG file.') );
+      }
+      else {
+        // Check for PNG-Signature (cf. http://www.libpng.org/pub/png/book/chapter08.html#png.ch08.div.2) in the
+        // response body.
+        $this->assertNoRaw( chr(137) . chr(80) . chr(78) . chr(71) . chr(13) . chr(10) . chr(26) . chr(10), t('No PNG signature found in the response body.') );
+      }
     }
 
     $GLOBALS['script_path'] = $script_path_original;