diff --git a/README b/README
index 5a99cea7c..f10ec0b3d 100644
--- a/README
+++ b/README
@@ -913,13 +913,17 @@ Images with captions
 --------------------
 
 An image occurring by itself in a paragraph will be rendered as
-a figure with a caption.  (In LaTeX, a figure environment will be
+a figure with a caption.[^5] (In LaTeX, a figure environment will be
 used; in HTML, the image will be placed in a `div` with class
 `figure`, together with a caption in a `p` with class `caption`.)
 The image's alt text will be used as the caption.
 
     ![This is the caption](/url/of/image.png)
 
+[^5]: This feature is not yet implemented for RTF, OpenDocument, or
+    ODT. In those formats, you'll just get an image in a paragraph by
+    itself, with no caption.
+
 If you just want a regular inline image, just make sure it is not
 the only thing in the paragraph. One way to do this is to insert a
 nonbreaking space after the image: