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/G6fJ4tqrcAg",
"published": "2025-11-08T13:31:09Z",
"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/puVcY0MOPKE",
"published": "2025-11-08T13:31:09Z",
"content": "no description",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/4af24a14-b86b-4e0f-8cc2-79466104e1c8.png"
}
}
}
mastodon
{
"id": "115514321762132090",
"created_at": "2025-11-08T13:31:09.000Z",
"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/puVcY0MOPKE",
"url": "http://pasture-one-actor/object/puVcY0MOPKE",
"replies_count": 0,
"reblogs_count": 0,
"favourites_count": 0,
"quotes_count": 0,
"edited_at": null,
"favourited": false,
"reblogged": false,
"muted": false,
"bookmarked": false,
"content": "no description",
"filtered": [],
"reblog": null,
"account": {
"id": "115514309622755922",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-11-08T00:00:00.000Z",
"note": "",
"url": "http://pasture-one-actor/actor",
"uri": "http://pasture-one-actor/actor",
"avatar": "http://localhost:2970/system/avatars/original/missing.png",
"avatar_static": "http://localhost:2970/system/avatars/original/missing.png",
"header": "http://localhost:2970/system/headers/original/missing.png",
"header_static": "http://localhost:2970/system/headers/original/missing.png",
"followers_count": 0,
"following_count": 0,
"statuses_count": 71,
"last_status_at": "2025-11-08",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115514321756187309",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/514/321/756/187/309/original/fe0a410adfeb3573.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/514/321/756/187/309/small/fe0a410adfeb3573.png",
"remote_url": "http://pasture-one-actor/images/4af24a14-b86b-4e0f-8cc2-79466104e1c8.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": "U1D.d9%|fQ%|%|j[fQj[fQfQfQfQ%|j[fQj["
}
],
"mentions": [],
"tags": [],
"emojis": [],
"quote": null,
"card": null,
"poll": null,
"quote_approval": {
"automatic": [],
"manual": [],
"current_user": "denied"
}
}
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/ihFlOsAlgUg",
"published": "2025-11-08T13:31:10Z",
"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/5FQx2LzES0E",
"published": "2025-11-08T13:31:10Z",
"content": "name, summary and content",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/e261037c-6e37-4104-b143-c79c8ebd8698.png",
"name": "name",
"summary": "summary",
"content": "content"
}
}
}
mastodon
{
"id": "115514321819391660",
"created_at": "2025-11-08T13:31:10.000Z",
"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/5FQx2LzES0E",
"url": "http://pasture-one-actor/object/5FQx2LzES0E",
"replies_count": 0,
"reblogs_count": 0,
"favourites_count": 0,
"quotes_count": 0,
"edited_at": null,
"favourited": false,
"reblogged": false,
"muted": false,
"bookmarked": false,
"content": "name, summary and content",
"filtered": [],
"reblog": null,
"account": {
"id": "115514309622755922",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-11-08T00:00:00.000Z",
"note": "",
"url": "http://pasture-one-actor/actor",
"uri": "http://pasture-one-actor/actor",
"avatar": "http://localhost:2970/system/avatars/original/missing.png",
"avatar_static": "http://localhost:2970/system/avatars/original/missing.png",
"header": "http://localhost:2970/system/headers/original/missing.png",
"header_static": "http://localhost:2970/system/headers/original/missing.png",
"followers_count": 0,
"following_count": 0,
"statuses_count": 72,
"last_status_at": "2025-11-08",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115514321813650602",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/514/321/813/650/602/original/2ebd408b17ba94d9.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/514/321/813/650/602/small/2ebd408b17ba94d9.png",
"remote_url": "http://pasture-one-actor/images/e261037c-6e37-4104-b143-c79c8ebd8698.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": "U1OMiF~lfQ~l~lj@fQj@fQfQfQfQ~lj@fQj@"
}
],
"mentions": [],
"tags": [],
"emojis": [],
"quote": null,
"card": null,
"poll": null,
"quote_approval": {
"automatic": [],
"manual": [],
"current_user": "denied"
}
}
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/_93-_5kFy9o",
"published": "2025-11-08T13:31:10Z",
"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/Rz0XTelEJcU",
"published": "2025-11-08T13:31:10Z",
"content": "only name",
"attachment": [
{
"type": "Image",
"url": "http://pasture-one-actor/assets/FediverseLogo.png",
"name": "name",
"imageType": "image/jpeg"
}
]
}
}
mastodon
{
"id": "115514321889280039",
"created_at": "2025-11-08T13:31:10.000Z",
"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/Rz0XTelEJcU",
"url": "http://pasture-one-actor/object/Rz0XTelEJcU",
"replies_count": 0,
"reblogs_count": 0,
"favourites_count": 0,
"quotes_count": 0,
"edited_at": null,
"favourited": false,
"reblogged": false,
"muted": false,
"bookmarked": false,
"content": "only name",
"filtered": [],
"reblog": null,
"account": {
"id": "115514309622755922",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-11-08T00:00:00.000Z",
"note": "",
"url": "http://pasture-one-actor/actor",
"uri": "http://pasture-one-actor/actor",
"avatar": "http://localhost:2970/system/avatars/original/missing.png",
"avatar_static": "http://localhost:2970/system/avatars/original/missing.png",
"header": "http://localhost:2970/system/headers/original/missing.png",
"header_static": "http://localhost:2970/system/headers/original/missing.png",
"followers_count": 0,
"following_count": 0,
"statuses_count": 73,
"last_status_at": "2025-11-08",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115514321875177446",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/514/321/875/177/446/original/e9790107d0cb43bd.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/514/321/875/177/446/small/e9790107d0cb43bd.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": "UOEVB3.}4.T=}fjEEVw[4=K[RUw~9,O?V?bV"
}
],
"mentions": [],
"tags": [],
"emojis": [],
"quote": null,
"card": null,
"poll": null,
"quote_approval": {
"automatic": [],
"manual": [],
"current_user": "denied"
}
}
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/a62WENhsR2A",
"published": "2025-11-08T13:31:11Z",
"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/5cD13Plv4tw",
"published": "2025-11-08T13:31:11Z",
"content": "only summary",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/696f6634-18ac-42d9-b526-cc67293c25a6.png",
"name": "name",
"summary": "summary",
"content": "content"
}
}
}
mastodon
{
"id": "115514321944845908",
"created_at": "2025-11-08T13:31:11.000Z",
"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/5cD13Plv4tw",
"url": "http://pasture-one-actor/object/5cD13Plv4tw",
"replies_count": 0,
"reblogs_count": 0,
"favourites_count": 0,
"quotes_count": 0,
"edited_at": null,
"favourited": false,
"reblogged": false,
"muted": false,
"bookmarked": false,
"content": "only summary",
"filtered": [],
"reblog": null,
"account": {
"id": "115514309622755922",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-11-08T00:00:00.000Z",
"note": "",
"url": "http://pasture-one-actor/actor",
"uri": "http://pasture-one-actor/actor",
"avatar": "http://localhost:2970/system/avatars/original/missing.png",
"avatar_static": "http://localhost:2970/system/avatars/original/missing.png",
"header": "http://localhost:2970/system/headers/original/missing.png",
"header_static": "http://localhost:2970/system/headers/original/missing.png",
"followers_count": 0,
"following_count": 0,
"statuses_count": 74,
"last_status_at": "2025-11-08",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115514321938504032",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/514/321/938/504/032/original/05aa39910f27af59.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/514/321/938/504/032/small/05aa39910f27af59.png",
"remote_url": "http://pasture-one-actor/images/696f6634-18ac-42d9-b526-cc67293c25a6.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": "U0B_0b-AfQ-A-AjtfQjtfQfQfQfQ-AjtfQjt"
}
],
"mentions": [],
"tags": [],
"emojis": [],
"quote": null,
"card": null,
"poll": null,
"quote_approval": {
"automatic": [],
"manual": [],
"current_user": "denied"
}
}
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/jNe6nI9CZ0w",
"published": "2025-11-08T13:31:12Z",
"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/LT1H2t2eQi4",
"published": "2025-11-08T13:31:12Z",
"content": "only content",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/6c57ef3d-04a5-4745-b55b-e9bf5e9a8661.png",
"content": "content"
}
}
}
mastodon
{
"id": "115514322005045183",
"created_at": "2025-11-08T13:31:12.000Z",
"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/LT1H2t2eQi4",
"url": "http://pasture-one-actor/object/LT1H2t2eQi4",
"replies_count": 0,
"reblogs_count": 0,
"favourites_count": 0,
"quotes_count": 0,
"edited_at": null,
"favourited": false,
"reblogged": false,
"muted": false,
"bookmarked": false,
"content": "only content",
"filtered": [],
"reblog": null,
"account": {
"id": "115514309622755922",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-11-08T00:00:00.000Z",
"note": "",
"url": "http://pasture-one-actor/actor",
"uri": "http://pasture-one-actor/actor",
"avatar": "http://localhost:2970/system/avatars/original/missing.png",
"avatar_static": "http://localhost:2970/system/avatars/original/missing.png",
"header": "http://localhost:2970/system/headers/original/missing.png",
"header_static": "http://localhost:2970/system/headers/original/missing.png",
"followers_count": 0,
"following_count": 0,
"statuses_count": 75,
"last_status_at": "2025-11-08",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115514321998134266",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/514/321/998/134/266/original/2614afb2304d1ce1.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/514/321/998/134/266/small/2614afb2304d1ce1.png",
"remote_url": "http://pasture-one-actor/images/6c57ef3d-04a5-4745-b55b-e9bf5e9a8661.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": "U2G;51$XfQ$X$XjufQjufQfQfQfQ$XjufQju"
}
],
"mentions": [],
"tags": [],
"emojis": [],
"quote": null,
"card": null,
"poll": null,
"quote_approval": {
"automatic": [],
"manual": [],
"current_user": "denied"
}
}
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/HIvaBklFI38",
"published": "2025-11-08T13:31:13Z",
"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/sK-CShhqwPQ",
"published": "2025-11-08T13:31:13Z",
"content": "no comment in attachment; reused image",
"attachment": [
{
"type": "Image",
"url": "http://pasture-one-actor/assets/FediverseLogo.png"
}
]
}
}
mastodon
{
"id": "115514322069959638",
"created_at": "2025-11-08T13:31:13.000Z",
"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/sK-CShhqwPQ",
"url": "http://pasture-one-actor/object/sK-CShhqwPQ",
"replies_count": 0,
"reblogs_count": 0,
"favourites_count": 0,
"quotes_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": "115514309622755922",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-11-08T00:00:00.000Z",
"note": "",
"url": "http://pasture-one-actor/actor",
"uri": "http://pasture-one-actor/actor",
"avatar": "http://localhost:2970/system/avatars/original/missing.png",
"avatar_static": "http://localhost:2970/system/avatars/original/missing.png",
"header": "http://localhost:2970/system/headers/original/missing.png",
"header_static": "http://localhost:2970/system/headers/original/missing.png",
"followers_count": 0,
"following_count": 0,
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