Image Description¶
The Image type is defined in ActivityStreams Vocabulary.
In this support table, we only consider how the image description, commonly called AltText is handled. Image descriptions are important from an accessibility standpoint, see WCAG 2.2. Text Alternatives.
It seems that certain implementations, e.g. misskey, store the image description on a per image URL basis and not for every instance of an image reference.
Examples¶
Example 1¶
activity
{
"@context": [
"https://www.w3.org/ns/activitystreams",
{
"Hashtag": "as:Hashtag",
"sensitive": "as:sensitive"
}
],
"type": "Create",
"actor": "http://pasture-one-actor/actor",
"to": [
"http://mastodon/users/hippo",
"https://www.w3.org/ns/activitystreams#Public"
],
"id": "http://pasture-one-actor/activity/VaIyBPT_7Yo",
"published": "2025-10-23T11:08:59Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/users/hippo"
],
"id": "http://pasture-one-actor/object/pCvj15IXoHc",
"published": "2025-10-23T11:08:59Z",
"content": "no description",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/508f2977-c0f4-4568-841c-9002f8cdc0e0.png"
}
}
}
mastodon
{
"id": "115423165771999834",
"created_at": "2025-10-23T11:08:59.000Z",
"in_reply_to_id": null,
"in_reply_to_account_id": null,
"sensitive": false,
"spoiler_text": "",
"visibility": "public",
"language": null,
"uri": "http://pasture-one-actor/object/pCvj15IXoHc",
"url": "http://pasture-one-actor/object/pCvj15IXoHc",
"replies_count": 0,
"reblogs_count": 0,
"favourites_count": 0,
"edited_at": null,
"favourited": false,
"reblogged": false,
"muted": false,
"bookmarked": false,
"content": "no description",
"filtered": [],
"reblog": null,
"account": {
"id": "115423154430999947",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-10-23T00:00:00.000Z",
"note": "",
"url": "http://pasture-one-actor/actor",
"uri": "http://pasture-one-actor/actor",
"avatar": "http://mastodon/avatars/original/missing.png",
"avatar_static": "http://mastodon/avatars/original/missing.png",
"header": "http://mastodon/headers/original/missing.png",
"header_static": "http://mastodon/headers/original/missing.png",
"followers_count": 0,
"following_count": 0,
"statuses_count": 71,
"last_status_at": "2025-10-23",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115423165765313703",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/423/165/765/313/703/original/b7c3406c4557e01e.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/423/165/765/313/703/small/b7c3406c4557e01e.png",
"remote_url": "http://pasture-one-actor/images/508f2977-c0f4-4568-841c-9002f8cdc0e0.png",
"preview_remote_url": null,
"text_url": null,
"meta": {
"original": {
"width": 40,
"height": 40,
"size": "40x40",
"aspect": 1.0
},
"small": {
"width": 40,
"height": 40,
"size": "40x40",
"aspect": 1.0
}
},
"description": null,
"blurhash": "U27RBoq7fQq7q7fjfQfjfQfQfQfQq7fjfQfj"
}
],
"mentions": [],
"tags": [],
"emojis": [],
"quote": null,
"card": null,
"poll": null
}
Example 2¶
activity
{
"@context": [
"https://www.w3.org/ns/activitystreams",
{
"Hashtag": "as:Hashtag",
"sensitive": "as:sensitive"
}
],
"type": "Create",
"actor": "http://pasture-one-actor/actor",
"to": [
"http://mastodon/users/hippo",
"https://www.w3.org/ns/activitystreams#Public"
],
"id": "http://pasture-one-actor/activity/PmA4sG7S3bI",
"published": "2025-10-23T11:09:00Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/users/hippo"
],
"id": "http://pasture-one-actor/object/G8wHdz98MuQ",
"published": "2025-10-23T11:09:00Z",
"content": "name, summary and content",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/cac21fe8-0bf5-46b7-935b-831fbf57c350.png",
"name": "name",
"summary": "summary",
"content": "content"
}
}
}
mastodon
{
"id": "115423165825456475",
"created_at": "2025-10-23T11:09:00.000Z",
"in_reply_to_id": null,
"in_reply_to_account_id": null,
"sensitive": false,
"spoiler_text": "",
"visibility": "public",
"language": null,
"uri": "http://pasture-one-actor/object/G8wHdz98MuQ",
"url": "http://pasture-one-actor/object/G8wHdz98MuQ",
"replies_count": 0,
"reblogs_count": 0,
"favourites_count": 0,
"edited_at": null,
"favourited": false,
"reblogged": false,
"muted": false,
"bookmarked": false,
"content": "name, summary and content",
"filtered": [],
"reblog": null,
"account": {
"id": "115423154430999947",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-10-23T00:00:00.000Z",
"note": "",
"url": "http://pasture-one-actor/actor",
"uri": "http://pasture-one-actor/actor",
"avatar": "http://mastodon/avatars/original/missing.png",
"avatar_static": "http://mastodon/avatars/original/missing.png",
"header": "http://mastodon/headers/original/missing.png",
"header_static": "http://mastodon/headers/original/missing.png",
"followers_count": 0,
"following_count": 0,
"statuses_count": 72,
"last_status_at": "2025-10-23",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115423165819996316",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/423/165/819/996/316/original/01dcb87fd1573704.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/423/165/819/996/316/small/01dcb87fd1573704.png",
"remote_url": "http://pasture-one-actor/images/cac21fe8-0bf5-46b7-935b-831fbf57c350.png",
"preview_remote_url": null,
"text_url": null,
"meta": {
"original": {
"width": 40,
"height": 40,
"size": "40x40",
"aspect": 1.0
},
"small": {
"width": 40,
"height": 40,
"size": "40x40",
"aspect": 1.0
}
},
"description": "summary",
"blurhash": "U2R+n^}xfQ}x}xj[fQj[fQfQfQfQ}xj[fQj["
}
],
"mentions": [],
"tags": [],
"emojis": [],
"quote": null,
"card": null,
"poll": null
}
Example 3¶
activity
{
"@context": [
"https://www.w3.org/ns/activitystreams",
{
"Hashtag": "as:Hashtag",
"sensitive": "as:sensitive"
}
],
"type": "Create",
"actor": "http://pasture-one-actor/actor",
"to": [
"http://mastodon/users/hippo",
"https://www.w3.org/ns/activitystreams#Public"
],
"id": "http://pasture-one-actor/activity/YCmo9C_0-GU",
"published": "2025-10-23T11:09:00Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/users/hippo"
],
"id": "http://pasture-one-actor/object/O316_xazUZc",
"published": "2025-10-23T11:09:00Z",
"content": "only name",
"attachment": [
{
"type": "Image",
"url": "http://pasture-one-actor/assets/FediverseLogo.png",
"name": "name",
"imageType": "image/jpeg"
}
]
}
}
mastodon
{
"id": "115423165907820679",
"created_at": "2025-10-23T11:09:00.000Z",
"in_reply_to_id": null,
"in_reply_to_account_id": null,
"sensitive": false,
"spoiler_text": "",
"visibility": "public",
"language": null,
"uri": "http://pasture-one-actor/object/O316_xazUZc",
"url": "http://pasture-one-actor/object/O316_xazUZc",
"replies_count": 0,
"reblogs_count": 0,
"favourites_count": 0,
"edited_at": null,
"favourited": false,
"reblogged": false,
"muted": false,
"bookmarked": false,
"content": "only name",
"filtered": [],
"reblog": null,
"account": {
"id": "115423154430999947",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-10-23T00:00:00.000Z",
"note": "",
"url": "http://pasture-one-actor/actor",
"uri": "http://pasture-one-actor/actor",
"avatar": "http://mastodon/avatars/original/missing.png",
"avatar_static": "http://mastodon/avatars/original/missing.png",
"header": "http://mastodon/headers/original/missing.png",
"header_static": "http://mastodon/headers/original/missing.png",
"followers_count": 0,
"following_count": 0,
"statuses_count": 73,
"last_status_at": "2025-10-23",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115423165890118711",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/423/165/890/118/711/original/c119584335b2213f.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/423/165/890/118/711/small/c119584335b2213f.png",
"remote_url": "http://pasture-one-actor/assets/FediverseLogo.png",
"preview_remote_url": null,
"text_url": null,
"meta": {
"original": {
"width": 1548,
"height": 1548,
"size": "1548x1548",
"aspect": 1.0
},
"small": {
"width": 480,
"height": 480,
"size": "480x480",
"aspect": 1.0
}
},
"description": "name",
"blurhash": "UOEVB2.}4.T=}fjEEVw[4=K[RUw~9,TJV?bW"
}
],
"mentions": [],
"tags": [],
"emojis": [],
"quote": null,
"card": null,
"poll": null
}
Example 4¶
activity
{
"@context": [
"https://www.w3.org/ns/activitystreams",
{
"Hashtag": "as:Hashtag",
"sensitive": "as:sensitive"
}
],
"type": "Create",
"actor": "http://pasture-one-actor/actor",
"to": [
"http://mastodon/users/hippo",
"https://www.w3.org/ns/activitystreams#Public"
],
"id": "http://pasture-one-actor/activity/4oQu5QkhIWQ",
"published": "2025-10-23T11:09:01Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/users/hippo"
],
"id": "http://pasture-one-actor/object/PFqUX-lv34k",
"published": "2025-10-23T11:09:01Z",
"content": "only summary",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/0de515f0-cc71-40a0-91a8-06e4b20a8a1d.png",
"name": "name",
"summary": "summary",
"content": "content"
}
}
}
mastodon
{
"id": "115423165950661905",
"created_at": "2025-10-23T11:09:01.000Z",
"in_reply_to_id": null,
"in_reply_to_account_id": null,
"sensitive": false,
"spoiler_text": "",
"visibility": "public",
"language": null,
"uri": "http://pasture-one-actor/object/PFqUX-lv34k",
"url": "http://pasture-one-actor/object/PFqUX-lv34k",
"replies_count": 0,
"reblogs_count": 0,
"favourites_count": 0,
"edited_at": null,
"favourited": false,
"reblogged": false,
"muted": false,
"bookmarked": false,
"content": "only summary",
"filtered": [],
"reblog": null,
"account": {
"id": "115423154430999947",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-10-23T00:00:00.000Z",
"note": "",
"url": "http://pasture-one-actor/actor",
"uri": "http://pasture-one-actor/actor",
"avatar": "http://mastodon/avatars/original/missing.png",
"avatar_static": "http://mastodon/avatars/original/missing.png",
"header": "http://mastodon/headers/original/missing.png",
"header_static": "http://mastodon/headers/original/missing.png",
"followers_count": 0,
"following_count": 0,
"statuses_count": 74,
"last_status_at": "2025-10-23",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115423165944303481",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/423/165/944/303/481/original/2be7aaab3cce6f17.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/423/165/944/303/481/small/2be7aaab3cce6f17.png",
"remote_url": "http://pasture-one-actor/images/0de515f0-cc71-40a0-91a8-06e4b20a8a1d.png",
"preview_remote_url": null,
"text_url": null,
"meta": {
"original": {
"width": 40,
"height": 40,
"size": "40x40",
"aspect": 1.0
},
"small": {
"width": 40,
"height": 40,
"size": "40x40",
"aspect": 1.0
}
},
"description": "summary",
"blurhash": "U11l{nlzfQlzlzfjfQfjfQfQfQfQlzfjfQfj"
}
],
"mentions": [],
"tags": [],
"emojis": [],
"quote": null,
"card": null,
"poll": null
}
Example 5¶
activity
{
"@context": [
"https://www.w3.org/ns/activitystreams",
{
"Hashtag": "as:Hashtag",
"sensitive": "as:sensitive"
}
],
"type": "Create",
"actor": "http://pasture-one-actor/actor",
"to": [
"http://mastodon/users/hippo",
"https://www.w3.org/ns/activitystreams#Public"
],
"id": "http://pasture-one-actor/activity/gw913ya4f1A",
"published": "2025-10-23T11:09:02Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/users/hippo"
],
"id": "http://pasture-one-actor/object/QwjlykwcVzU",
"published": "2025-10-23T11:09:02Z",
"content": "only content",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/e8aa65c6-6d78-46d2-9a0c-1a5208da2ae3.png",
"content": "content"
}
}
}
mastodon
{
"id": "115423166006027385",
"created_at": "2025-10-23T11:09:02.000Z",
"in_reply_to_id": null,
"in_reply_to_account_id": null,
"sensitive": false,
"spoiler_text": "",
"visibility": "public",
"language": null,
"uri": "http://pasture-one-actor/object/QwjlykwcVzU",
"url": "http://pasture-one-actor/object/QwjlykwcVzU",
"replies_count": 0,
"reblogs_count": 0,
"favourites_count": 0,
"edited_at": null,
"favourited": false,
"reblogged": false,
"muted": false,
"bookmarked": false,
"content": "only content",
"filtered": [],
"reblog": null,
"account": {
"id": "115423154430999947",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-10-23T00:00:00.000Z",
"note": "",
"url": "http://pasture-one-actor/actor",
"uri": "http://pasture-one-actor/actor",
"avatar": "http://mastodon/avatars/original/missing.png",
"avatar_static": "http://mastodon/avatars/original/missing.png",
"header": "http://mastodon/headers/original/missing.png",
"header_static": "http://mastodon/headers/original/missing.png",
"followers_count": 0,
"following_count": 0,
"statuses_count": 75,
"last_status_at": "2025-10-23",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115423165999600446",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/423/165/999/600/446/original/d3184d723d48340e.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/423/165/999/600/446/small/d3184d723d48340e.png",
"remote_url": "http://pasture-one-actor/images/e8aa65c6-6d78-46d2-9a0c-1a5208da2ae3.png",
"preview_remote_url": null,
"text_url": null,
"meta": {
"original": {
"width": 40,
"height": 40,
"size": "40x40",
"aspect": 1.0
},
"small": {
"width": 40,
"height": 40,
"size": "40x40",
"aspect": 1.0
}
},
"description": null,
"blurhash": "U2SErC~QfQ~Q~Qj@fQj@fQfQfQfQ~Qj@fQj@"
}
],
"mentions": [],
"tags": [],
"emojis": [],
"quote": null,
"card": null,
"poll": null
}
Example 6¶
activity
{
"@context": [
"https://www.w3.org/ns/activitystreams",
{
"Hashtag": "as:Hashtag",
"sensitive": "as:sensitive"
}
],
"type": "Create",
"actor": "http://pasture-one-actor/actor",
"to": [
"http://mastodon/users/hippo",
"https://www.w3.org/ns/activitystreams#Public"
],
"id": "http://pasture-one-actor/activity/UtnrnTz9u1s",
"published": "2025-10-23T11:09:03Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/users/hippo"
],
"id": "http://pasture-one-actor/object/bHtC_FaC2go",
"published": "2025-10-23T11:09:03Z",
"content": "no comment in attachment; reused image",
"attachment": [
{
"type": "Image",
"url": "http://pasture-one-actor/assets/FediverseLogo.png"
}
]
}
}
mastodon
{
"id": "115423166072894887",
"created_at": "2025-10-23T11:09:03.000Z",
"in_reply_to_id": null,
"in_reply_to_account_id": null,
"sensitive": false,
"spoiler_text": "",
"visibility": "public",
"language": null,
"uri": "http://pasture-one-actor/object/bHtC_FaC2go",
"url": "http://pasture-one-actor/object/bHtC_FaC2go",
"replies_count": 0,
"reblogs_count": 0,
"favourites_count": 0,
"edited_at": null,
"favourited": false,
"reblogged": false,
"muted": false,
"bookmarked": false,
"content": "no comment in attachment; reused image",
"filtered": [],
"reblog": null,
"account": {
"id": "115423154430999947",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-10-23T00:00:00.000Z",
"note": "",
"url": "http://pasture-one-actor/actor",
"uri": "http://pasture-one-actor/actor",
"avatar": "http://mastodon/avatars/original/missing.png",
"avatar_static": "http://mastodon/avatars/original/missing.png",
"header": "http://mastodon/headers/original/missing.png",
"header_static": "http://mastodon/headers/original/missing.png",
"followers_count": 0,
"following_count": 0,
"statuses_count": 76,
"last_status_at": "2025-10-23",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115423166056085613",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/423/166/056/085/613/original/8dae9d59f6114edf.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/423/166/056/085/613/small/8dae9d59f6114edf.png",
"remote_url": "http://pasture-one-actor/assets/FediverseLogo.png",
"preview_remote_url": null,
"text_url": null,
"meta": {
"original": {
"width": 1548,
"height": 1548,
"size": "1548x1548",
"aspect": 1.0
},
"small": {
"width": 480,
"height": 480,
"size": "480x480",
"aspect": 1.0
}
},
"description": null,
"blurhash": "UOEVB2.}4.T=}fjEEVw[4=K[RUw~9,TJV?bW"
}
],
"mentions": [],
"tags": [],
"emojis": [],
"quote": null,
"card": null,
"poll": null
}