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/users/hippo"
],
"id": "http://pasture-one-actor/activity/wMG5vYTpF90",
"published": "2025-12-07T10:22:21Z",
"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/faUd7edzrIk",
"published": "2025-12-07T10:22:21Z",
"content": "no description",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/058c235a-b25f-478b-a3a5-e8d1b5f14072.png"
}
}
}
mastodon
{
"id": "115677786400561695",
"created_at": "2025-12-07T10:22:21.000Z",
"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/faUd7edzrIk",
"url": "http://pasture-one-actor/object/faUd7edzrIk",
"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": "115677774182613185",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-12-07T00:00:00.000Z",
"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": "2025-12-07",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115677786395742474",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/677/786/395/742/474/original/78d1ca02d1ef4dcb.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/677/786/395/742/474/small/78d1ca02d1ef4dcb.png",
"remote_url": "http://pasture-one-actor/images/058c235a-b25f-478b-a3a5-e8d1b5f14072.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": "U1IjbF?^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/users/hippo"
],
"id": "http://pasture-one-actor/activity/8FePwASU1iM",
"published": "2025-12-07T10:22:22Z",
"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/j0j3oeD_FMo",
"published": "2025-12-07T10:22:22Z",
"content": "name, summary and content",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/29dcd75e-2a34-43fc-a792-9fda3e35f998.png",
"name": "name",
"summary": "summary",
"content": "content"
}
}
}
mastodon
{
"id": "115677786468579815",
"created_at": "2025-12-07T10:22:22.000Z",
"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/j0j3oeD_FMo",
"url": "http://pasture-one-actor/object/j0j3oeD_FMo",
"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": "115677774182613185",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-12-07T00:00:00.000Z",
"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": "2025-12-07",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115677786462601614",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/677/786/462/601/614/original/ff71954de24bcb88.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/677/786/462/601/614/small/ff71954de24bcb88.png",
"remote_url": "http://pasture-one-actor/images/29dcd75e-2a34-43fc-a792-9fda3e35f998.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": "U2Lo:|?1fQ?1?1j[fQj[fQfQfQfQ?1j[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/users/hippo"
],
"id": "http://pasture-one-actor/activity/WLeuJRoyfv4",
"published": "2025-12-07T10:22:23Z",
"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/pTtKEREBK9Y",
"published": "2025-12-07T10:22:23Z",
"content": "only name",
"attachment": [
{
"type": "Image",
"url": "http://pasture-one-actor/assets/FediverseLogo.png",
"name": "name",
"imageType": "image/jpeg"
}
]
}
}
mastodon
{
"id": "115677786538168135",
"created_at": "2025-12-07T10:22:23.000Z",
"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/pTtKEREBK9Y",
"url": "http://pasture-one-actor/object/pTtKEREBK9Y",
"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": "115677774182613185",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-12-07T00:00:00.000Z",
"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": "2025-12-07",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115677786524022476",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/677/786/524/022/476/original/b207a29e7b0b83f9.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/677/786/524/022/476/small/b207a29e7b0b83f9.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/users/hippo"
],
"id": "http://pasture-one-actor/activity/VkyqEQAsXso",
"published": "2025-12-07T10:22:24Z",
"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/isO48X2sy8g",
"published": "2025-12-07T10:22:24Z",
"content": "only summary",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/1f9eca8b-3d57-4c36-a418-6ab7f3471d37.png",
"summary": "summary"
}
}
}
mastodon
{
"id": "115677786590703794",
"created_at": "2025-12-07T10:22:24.000Z",
"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/isO48X2sy8g",
"url": "http://pasture-one-actor/object/isO48X2sy8g",
"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": "115677774182613185",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-12-07T00:00:00.000Z",
"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": "2025-12-07",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115677786583362999",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/677/786/583/362/999/original/3928ce94df12c43b.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/677/786/583/362/999/small/3928ce94df12c43b.png",
"remote_url": "http://pasture-one-actor/images/1f9eca8b-3d57-4c36-a418-6ab7f3471d37.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": "U2Gn_|%~fQ%~%~j[fQj[fQfQfQfQ%~j[fQj["
}
],
"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/users/hippo"
],
"id": "http://pasture-one-actor/activity/LPJs8y0baXI",
"published": "2025-12-07T10:22:25Z",
"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/wLGkZYpyeUo",
"published": "2025-12-07T10:22:25Z",
"content": "only content",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/aef0d861-4ad4-4cef-88aa-db33b6cf4a12.png",
"content": "content"
}
}
}
mastodon
{
"id": "115677786649162223",
"created_at": "2025-12-07T10:22:25.000Z",
"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/wLGkZYpyeUo",
"url": "http://pasture-one-actor/object/wLGkZYpyeUo",
"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": "115677774182613185",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-12-07T00:00:00.000Z",
"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": "2025-12-07",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115677786642474265",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/677/786/642/474/265/original/f0873c57dae56194.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/677/786/642/474/265/small/f0873c57dae56194.png",
"remote_url": "http://pasture-one-actor/images/aef0d861-4ad4-4cef-88aa-db33b6cf4a12.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": "U17~_}uafQuauafjfQfjfQfQfQfQuafjfQfj"
}
],
"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/users/hippo"
],
"id": "http://pasture-one-actor/activity/PKJIhB8eePo",
"published": "2025-12-07T10:22:26Z",
"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/h69KBUg8AfA",
"published": "2025-12-07T10:22:26Z",
"content": "no comment in attachment; reused image",
"attachment": [
{
"type": "Image",
"url": "http://pasture-one-actor/assets/FediverseLogo.png"
}
]
}
}
mastodon
{
"id": "115677786719623730",
"created_at": "2025-12-07T10:22:26.000Z",
"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/h69KBUg8AfA",
"url": "http://pasture-one-actor/object/h69KBUg8AfA",
"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": "115677774182613185",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-12-07T00:00:00.000Z",
"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": 76,
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