diff --git a/app/code/core/Mage/Adminhtml/controllers/Cms/Wysiwyg/ImagesController.php b/app/code/core/Mage/Adminhtml/controllers/Cms/Wysiwyg/ImagesController.php
index 5b1bf2d3c0a71..97442f3ecbed9 100644
--- a/app/code/core/Mage/Adminhtml/controllers/Cms/Wysiwyg/ImagesController.php
+++ b/app/code/core/Mage/Adminhtml/controllers/Cms/Wysiwyg/ImagesController.php
@@ -182,6 +182,7 @@ public function onInsertAction()
      */
     public function thumbnailAction()
     {
+        $this->getResponse()->disableOutput();
         $file = $this->getRequest()->getParam('file');
         $file = Mage::helper('Mage_Cms_Helper_Wysiwyg_Images')->idDecode($file);
         $thumb = $this->getStorage()->resizeOnTheFly($file);
diff --git a/app/code/core/Mage/Adminhtml/controllers/Cms/WysiwygController.php b/app/code/core/Mage/Adminhtml/controllers/Cms/WysiwygController.php
index caf3e505e00a9..2080997c113e8 100644
--- a/app/code/core/Mage/Adminhtml/controllers/Cms/WysiwygController.php
+++ b/app/code/core/Mage/Adminhtml/controllers/Cms/WysiwygController.php
@@ -40,6 +40,7 @@ class Mage_Adminhtml_Cms_WysiwygController extends Mage_Adminhtml_Controller_Act
      */
     public function directiveAction()
     {
+        $this->getResponse()->disableOutput();
         $directive = $this->getRequest()->getParam('___directive');
         $directive = Mage::helper('Mage_Core_Helper_Data')->urlDecode($directive);
         $url = Mage::getModel('Mage_Core_Model_Email_Template_Filter')->filter($directive);
diff --git a/app/code/core/Mage/Core/Controller/Response/Http.php b/app/code/core/Mage/Core/Controller/Response/Http.php
index db9796e9c2463..4b8debfe10ba1 100644
--- a/app/code/core/Mage/Core/Controller/Response/Http.php
+++ b/app/code/core/Mage/Core/Controller/Response/Http.php
@@ -39,6 +39,20 @@ class Mage_Core_Controller_Response_Http extends Zend_Controller_Response_Http
      */
     protected static $_transportObject = null;
 
+    /**
+     * @var bool
+     */
+    protected $_isOutputDisabled = false;
+
+    /**
+     * Disable response output; useful for situations where the response was already rendered such as
+     * with an image library that uses direct output.
+     */
+    public function disableOutput()
+    {
+        $this->_isOutputDisabled = true;
+    }
+
     /**
      * Fixes CGI only one Status header allowed bug
      *
@@ -77,10 +91,15 @@ public function sendHeaders()
         return parent::sendHeaders();
     }
 
+    /**
+     * Dispatch an event before the response is rendered and only render response if it is not disabled.
+     */
     public function sendResponse()
     {
         Mage::dispatchEvent('http_response_send_before', array('response'=>$this));
-        return parent::sendResponse();
+        if ( ! $this->_isOutputDisabled) {
+            return parent::sendResponse();
+        }
     }
 
     /**