Handle the case when an image is unavailable

otbox.py

@@ -126,10 +126,19 @@ def _mqtt_handler_picturetoscreen(self, deviceType, deviceId, payload):
         {{TESTBED}}/deviceType/box/deviceId/box1/cmd/picturetoscreen
         '''
         assert deviceType==DEVICETYPE_BOX
-        image = Image.open(requests.get(json.loads(payload)['url'], stream=True).raw)
-        image.thumbnail((480,320),Image.ANTIALIAS)
-        self._otbox.change_image_queue.put(image)
-        self._otbox.change_image_queue.join()
+        try:
+            image_url = json.loads(payload)['url']
+            response = requests.get(image_url, stream=True)
+            image = Image.open(response.raw)
+        except IOError:
+            # the image is not available now; skip this one
+            print('image at {0} is not available, '.format(image_url)
+                  + 'HTTP response code {0}'.format(response.status_code))
+            sys.stdout.flush()
+        else:
+            image.thumbnail((480,320),Image.ANTIALIAS)
+            self._otbox.change_image_queue.put(image)
+            self._otbox.change_image_queue.join()
         return {}
 
     def _mqtt_handler_colortoscreen(self, deviceType, deviceId, payload):