diff --git a/PIL/Image.py b/PIL/Image.py
index 1f968daf5..c22ab3955 100644
--- a/PIL/Image.py
+++ b/PIL/Image.py
@@ -1066,6 +1066,9 @@ class Image(object):
         in place.  If the image has already been loaded, this method has no
         effect.
 
+        Note: This method is not implemented for most images. It is
+        currently implemented only for JPEG and PCD images.
+
         :param mode: The requested mode.
         :param size: The requested size.
         """