Add some alternative fonts with more permissive licenses

proposals/4347-emoji-verification-images.md

@@ -122,6 +122,8 @@ proper attribution, which should be added to the spec text.
   original authors of the relevant images on OpenMojo might grant permission for
   use under a more permissive license if needed.) It would seem polite to
   contact OpenMojo either way before incorporating this change into the spec.
+  See the alternatives section for some other emoji sets that are released under
+  the more permissive CC-BY license.
 
 ## Alternatives
 
@@ -134,6 +136,14 @@ proper attribution, which should be added to the spec text.
   further improve consistency, but might make life difficult for client
   developers who are not able to render certain image types.
 
+* We could use a different emoji set for the images, especially if the CC BY-SA
+  license of OpenMoji is judged to be too restrictive. These emoji sets are
+  released under more permissive licenses:
+
+    * [Emojitwo](https://emojitwo.github.io)
+    * [twemoji](https://github.com/twitter/twemoji)
+    * [noto-emoji](https://github.com/googlefonts/noto-emoji)
+
 ## Security considerations
 
 This proposal is intended to improve security by making it easier for users to