width and height are not allowed on an Image; closes #467.

Author: evanp

ERRATA.md

@@ -8,4 +8,38 @@ This document includes errata for the [Activity Streams](https://www.w3.org/TR/a
 
 ## Activity Vocabulary
 
-- None yet reported.
+  - Example 80 has `Image` objects with `width` and `height` properties, which
+    are only allowed on `Link` objects. One alternative is to use `Link` objects
+    with the correct `height` and `width` as the `url` property for each `Image`
+    object.
+    
+    ```json
+    {
+      "@context": "https://www.w3.org/ns/activitystreams",
+      "summary": "A simple note",
+      "type": "Note",
+      "content": "A simple note",
+      "icon": [
+        {
+          "type": "Image",
+          "summary": "Note (16x16)",
+          "url": {
+            "type": "Link",
+            "href": "http://example.org/note1.png",
+            "width": 16,
+            "height": 16
+          }
+        },
+        {
+          "type": "Image",
+          "summary": "Note (32x32)",
+          "url": {
+            "type": "Link",
+            "href": "http://example.org/note2.png",
+            "width": 32,
+            "height": 32
+          }
+        }
+      ]
+    }
+    ```