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": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/ap/users/115690779630094807"
],
"id": "http://pasture-one-actor/activity/0X8tmaecMTw",
"published": "2025-12-09T17:48:24Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/ap/users/115690779630094807"
],
"id": "http://pasture-one-actor/object/zxNJIsiylrI",
"published": "2025-12-09T17:48:24Z",
"content": "no description",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/7d845e22-c3a8-409c-9fd5-268187875239.png"
}
}
}
mastodon
{
"id": "115690864980768538",
"created_at": "2025-12-09T17:48:24.000Z",
"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/zxNJIsiylrI",
"url": "http://pasture-one-actor/object/zxNJIsiylrI",
"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": "115690789512226218",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-12-09T00:00:00.000Z",
"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": "2025-12-09",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115690864974887899",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/690/864/974/887/899/original/5bd38336d62930ac.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/690/864/974/887/899/small/5bd38336d62930ac.png",
"remote_url": "http://pasture-one-actor/images/7d845e22-c3a8-409c-9fd5-268187875239.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": "U0ED_=?-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": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/ap/users/115690779630094807"
],
"id": "http://pasture-one-actor/activity/-w3XJnv9UIA",
"published": "2025-12-09T17:48:25Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/ap/users/115690779630094807"
],
"id": "http://pasture-one-actor/object/dlhnW_4HAbI",
"published": "2025-12-09T17:48:25Z",
"content": "name, summary and content",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/d6401196-334a-4b2e-966a-1e031b98c1d2.png",
"name": "name",
"summary": "summary",
"content": "content"
}
}
}
mastodon
{
"id": "115690865044431662",
"created_at": "2025-12-09T17:48:25.000Z",
"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/dlhnW_4HAbI",
"url": "http://pasture-one-actor/object/dlhnW_4HAbI",
"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": "115690789512226218",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-12-09T00:00:00.000Z",
"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": "2025-12-09",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115690865037731326",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/690/865/037/731/326/original/fc35977ce6aec25e.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/690/865/037/731/326/small/fc35977ce6aec25e.png",
"remote_url": "http://pasture-one-actor/images/d6401196-334a-4b2e-966a-1e031b98c1d2.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": "U1L.mE^nfQ^n^nj[fQj[fQfQfQfQ^nj[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": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/ap/users/115690779630094807"
],
"id": "http://pasture-one-actor/activity/p4Sbyj_IMTQ",
"published": "2025-12-09T17:48:26Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/ap/users/115690779630094807"
],
"id": "http://pasture-one-actor/object/NuO4wEoVw7U",
"published": "2025-12-09T17:48:26Z",
"content": "only name",
"attachment": [
{
"type": "Image",
"url": "http://pasture-one-actor/assets/FediverseLogo.png",
"name": "name",
"imageType": "image/jpeg"
}
]
}
}
mastodon
{
"id": "115690865113669390",
"created_at": "2025-12-09T17:48:26.000Z",
"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/NuO4wEoVw7U",
"url": "http://pasture-one-actor/object/NuO4wEoVw7U",
"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": "115690789512226218",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-12-09T00:00:00.000Z",
"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": "2025-12-09",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115690865097678510",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/690/865/097/678/510/original/67de6f75bbb0c1ca.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/690/865/097/678/510/small/67de6f75bbb0c1ca.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": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/ap/users/115690779630094807"
],
"id": "http://pasture-one-actor/activity/jgyZvKATz3M",
"published": "2025-12-09T17:48:27Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/ap/users/115690779630094807"
],
"id": "http://pasture-one-actor/object/WL_Lz-yrmF0",
"published": "2025-12-09T17:48:27Z",
"content": "only summary",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/029eab85-e273-4b97-b7e5-24827b07c657.png",
"summary": "summary"
}
}
}
mastodon
{
"id": "115690865166368318",
"created_at": "2025-12-09T17:48:27.000Z",
"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/WL_Lz-yrmF0",
"url": "http://pasture-one-actor/object/WL_Lz-yrmF0",
"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": "115690789512226218",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-12-09T00:00:00.000Z",
"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": "2025-12-09",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115690865159114811",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/690/865/159/114/811/original/58d6ae57bd82dd3f.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/690/865/159/114/811/small/58d6ae57bd82dd3f.png",
"remote_url": "http://pasture-one-actor/images/029eab85-e273-4b97-b7e5-24827b07c657.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": "U1Bas[y:fQy:y:fkfQfkfQfQfQfQy:fkfQfk"
}
],
"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": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/ap/users/115690779630094807"
],
"id": "http://pasture-one-actor/activity/OGos7uqjxmc",
"published": "2025-12-09T17:48:28Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/ap/users/115690779630094807"
],
"id": "http://pasture-one-actor/object/lgVMbOZU6WE",
"published": "2025-12-09T17:48:28Z",
"content": "only content",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/f868d715-52ca-41de-b61b-64bf6bbd78ed.png",
"content": "content"
}
}
}
mastodon
{
"id": "115690865225875364",
"created_at": "2025-12-09T17:48:28.000Z",
"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/lgVMbOZU6WE",
"url": "http://pasture-one-actor/object/lgVMbOZU6WE",
"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": "115690789512226218",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-12-09T00:00:00.000Z",
"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": "2025-12-09",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115690865219922514",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/690/865/219/922/514/original/989eb9158c472d7d.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/690/865/219/922/514/small/989eb9158c472d7d.png",
"remote_url": "http://pasture-one-actor/images/f868d715-52ca-41de-b61b-64bf6bbd78ed.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": "U0KnSS~qfQ~q~qj[fQj[fQfQfQfQ~qj[fQj["
}
],
"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": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/ap/users/115690779630094807"
],
"id": "http://pasture-one-actor/activity/50kZw3p4hIo",
"published": "2025-12-09T17:48:29Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://mastodon/ap/users/115690779630094807"
],
"id": "http://pasture-one-actor/object/aksia5Iz4Gc",
"published": "2025-12-09T17:48:29Z",
"content": "no comment in attachment; reused image",
"attachment": [
{
"type": "Image",
"url": "http://pasture-one-actor/assets/FediverseLogo.png"
}
]
}
}
mastodon
{
"id": "115690865295378613",
"created_at": "2025-12-09T17:48:29.000Z",
"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/aksia5Iz4Gc",
"url": "http://pasture-one-actor/object/aksia5Iz4Gc",
"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": "115690789512226218",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-12-09T00:00:00.000Z",
"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",
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