NIP-92: imeta tags for kind 0 picture and banner (#2494)

24.md

@@ -14,7 +14,7 @@ These are extra fields not specified in NIP-01 that may be present in the string
 
   - `display_name`: an alternative, bigger name with richer characters than `name`. `name` should always be set regardless of the presence of `display_name` in the metadata.
   - `website`: a web URL related in any way to the event author.
-  - `banner`: an URL to a wide (~1024x768) picture to be optionally displayed in the background of a profile screen.
+  - `banner`: an URL to a wide (~1024x768) picture to be optionally displayed in the background of a profile screen. It MAY be described by an `imeta` tag as in [NIP-92](92.md#profile-metadata).
   - `bot`: a boolean to clarify that the content is entirely or partially the result of automation, such as with chatbots or newsfeeds.
   - `birthday`: an object representing the author's birth date. The format is { "year": number, "month": number, "day": number }. Each field MAY be omitted.
 

92.md

@@ -43,3 +43,38 @@ When pasting URLs during post composition, the client MAY download the file
 and add this metadata before the post is sent.
 
 The client MAY ignore `imeta` tags that do not match the URL in the event content.
+
+## Profile metadata
+
+A kind `0` event MAY carry `imeta` tags describing the images named by the `picture` and `banner` fields of its stringified JSON content ([NIP-01](01.md), [NIP-24](24.md)). This gives profile images the same `fallback`, `blurhash`, `dim`, `alt`, and other [NIP-94](94.md) fields available to any other attachment.
+
+An `imeta` tag describes a field only when its `url` is exactly equal to that field's value. Tags whose `url` matches neither field SHOULD be ignored.
+
+```json
+{
+  "kind": 0,
+  "content": "{\"name\":\"luna\",\"picture\":\"https://blossom.example/1f2e...a9.jpg\",\"banner\":\"https://blossom.example/7c3d...04.webp\"}",
+  "tags": [
+    [
+      "imeta",
+      "url https://blossom.example/1f2e...a9.jpg",
+      "m image/jpeg",
+      "x 1f2e...a9",
+      "dim 400x400",
+      "blurhash LEHV6nWB2yk8pyo0adR*.7kCMdnj",
+      "fallback https://mirror.example/1f2e...a9.jpg"
+    ],
+    [
+      "imeta",
+      "url https://blossom.example/7c3d...04.webp",
+      "m image/webp",
+      "x 7c3d...04",
+      "dim 1500x500"
+    ]
+  ]
+}
+```
+
+Clients SHOULD try the declared `fallback` URLs when the primary URL fails to load.
+
+Since kind `0` is replaceable, clients publishing a new kind `0` SHOULD carry over the `imeta` tags for a `picture` or `banner` that hasn't changed, and drop the tags for images that are no longer in use.