diff --git a/68.md b/68.md
index 8a87848..2950712 100644
--- a/68.md
+++ b/68.md
@@ -59,7 +59,8 @@ They may contain multiple images to be displayed as a single post.
     ["p", "<32-bytes hex of a pubkey>", "<optional recommended relay URL>"],
 
     // Specify the media type for filters to allow clients to filter by supported kinds
-    ["m", "image/jpeg"]
+    ["m", "image/jpeg"],
+    ["x", "<sha256>"]
 
     // Hashtags
     ["t", "<tag>"],