Site icon federates as the post icon and shows up as an extra image on Misskey

[pfefferle]

Quick summary

Posts without a featured image federate with the site icon in the icon property. Misskey renders that as an extra low-resolution image on the post, so the site logo shows up under every post that has no image of its own.

Reported here: https://wordpress.org/support/topic/misskey-posts-include-additional-lo-res-images/

An example, a Note with an empty attachment array but an icon:

{
  "type": "Note",
  "attachment": [],
  "icon": {
    "type": "Image",
    "mediaType": "image/jpeg",
    "url": "https://dorkboy.ca/wp-content/uploads/2026/08/cropped-cropped-Robot-3-1-150x150.jpg"
  }
}

Why it happens

Nothing asks for an icon on a Note. Transformer\Base::to_object() walks every property the object supports and calls the matching getter if the transformer has one:

$getter = 'get_' . $var;

if ( \method_exists( $this, $getter ) ) {
	$value = \call_user_func( array( $this, $getter ) );

Base_Object has an icon property and Transformer\Post has get_icon(), so every post gets one. get_icon() uses the featured image and falls back to get_option( 'site_icon' ) at thumbnail size, which is where the 150x150 crop comes from.

Mastodon ignores icon on a Note, Misskey shows it, and both are defensible: AS2 describes icon as a small image representing the object.

get_icon() has a second, wanted use as the poster fallback for video attachments in Transformer\Base, so the method should stay either way.

Options

1. Drop the site_icon fallback from Transformer\Post::get_icon(). No featured image, no icon. Fixes the report and keeps a real thumbnail where there is one.
2. Stop mapping icon onto the object and keep get_icon() only for the video poster. A Note then never carries icon, on the grounds that attachment already carries the images.
3. Leave it. It is spec-legal and only one implementation surfaces it.

Option 1 looks like the smallest fix that addresses what was reported, since the complaint is specifically about the site logo appearing on posts that have no image. Option 2 is the stronger argument if we think a post should not advertise an icon at all.

Site owner impact

Fewer than 20% of the total website/platform users

Severity

Low

[pfefferle]

Correction on the summary above, the site icon is only half of it. get_icon() uses the featured image when there is one, at thumbnail size, while get_image() uses the same featured image at large. So a post with a featured image federates that image twice, once full size as image and once as a 150x150 icon. That is the low resolution duplicate in the report title. Posts without a featured image get the site icon instead, which is the example JSON above.

Both cases come from the same place, so the options are unchanged.

Useful for a workaround, and maybe for the fix: thumbnail is only ever used by get_icon(). get_image() and the attachment loop in Transformer\Base both use large, so the activitypub_get_image filter can single out the icon by its size argument.

[pfefferle]

Fixed in #3721, with option 2, and it grew a second half along the way.

Why option 2 and not option 1. Dropping the site_icon fallback only fixes posts without a featured image. A post that has one would still send it twice, once as image at large and once as icon at thumbnail, which is the lo-res duplicate in the title here. Option 2 covers both cases in one change.

The change is a rename. Transformer\Post::get_icon() is now get_media_icon(), because Base::transform_object_properties() maps each getter onto the property of the same name, so the name was the whole mechanism. The method stays, still protected, and keeps the video and podcast poster job.

Two things from the history that settled it. get_icon() arrived in #1053, "This adds Icon support for Audio and Video attachments", with exactly one consumer in the same diff, the attachment poster. Before that posts carried no icon at all, so the object property was never a decision, it came along with the naming convention. And FEP-b2b8 gives long-form text a representative image as image, further media as attachment, and uses icon only for the author's avatar in attributedTo. I went through all 51 issues on the FEP repo, open and closed, comments included: icon is not mentioned once, so there is no older revision we were following.

The second half: the featured image was going out twice too. Not just as icon, but as both image and attachment[0], at large in both. get_image() was added in #982 for FEP-b2b8 support, purely additively on top of the older attachment behaviour, so nothing decided those two should coexist either.

It now has one home, picked by whether the type is long-form:

• Article and Page send it as image and not as an attachment
• everything else, Note included, keeps it as an attachment and sends no image
• anything a filter invents for activitypub_post_object_type falls to the attachment side, which every implementation renders

That follows the FEP, where attachment is media that is part of the text, and a featured image is not in the content. It also needed a fix on our own side: Remote_Posts::extract_attachments() only read attachment, so it would have dropped the picture for every Article we cache. It now falls back to image, the way Embed::render() already did.

One thing still open. Mastodon renders attachment and I have not been able to check what it does with an Article that has image and no image attachment. If it shows nothing, the long-form half needs rethinking. It is separable from the icon fix, so that part can be reverted on its own. There is a step for it in the testing instructions on the PR.