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/yhwChEqEkOE",
"published": "2025-11-21T13:27:14Z",
"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/RaubgH3Z4sQ",
"published": "2025-11-21T13:27:14Z",
"content": "no description",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/4dcf8d70-161b-4aef-979c-02d252a7f5d6.png"
}
}
}
mastodon
{
"id": "115587916431728122",
"created_at": "2025-11-21T13:27:14.000Z",
"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/RaubgH3Z4sQ",
"url": "http://pasture-one-actor/object/RaubgH3Z4sQ",
"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": "115587904635725355",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-11-21T00:00:00.000Z",
"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": "2025-11-21",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115587916426307147",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/587/916/426/307/147/original/12dc9e40f1e87c0d.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/587/916/426/307/147/small/12dc9e40f1e87c0d.png",
"remote_url": "http://pasture-one-actor/images/4dcf8d70-161b-4aef-979c-02d252a7f5d6.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": "U2RDmW~jfQ~j~jj@fQj@fQfQfQfQ~jj@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/Qaj4VfpxSVA",
"published": "2025-11-21T13:27:15Z",
"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/ODJpxbFMAuA",
"published": "2025-11-21T13:27:15Z",
"content": "name, summary and content",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/0ebdd7bf-aad9-484a-89a2-060e4107d007.png",
"name": "name",
"summary": "summary",
"content": "content"
}
}
}
mastodon
{
"id": "115587916489022463",
"created_at": "2025-11-21T13:27:15.000Z",
"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/ODJpxbFMAuA",
"url": "http://pasture-one-actor/object/ODJpxbFMAuA",
"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": "115587904635725355",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-11-21T00:00:00.000Z",
"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": "2025-11-21",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115587916483703675",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/587/916/483/703/675/original/716c32717ec8a163.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/587/916/483/703/675/small/716c32717ec8a163.png",
"remote_url": "http://pasture-one-actor/images/0ebdd7bf-aad9-484a-89a2-060e4107d007.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": "U2Bu=UucfQucucfjfQfjfQfQfQfQucfjfQfj"
}
],
"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/FuoE-dzD0FE",
"published": "2025-11-21T13:27:16Z",
"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/M4To1nqoSz4",
"published": "2025-11-21T13:27:16Z",
"content": "only name",
"attachment": [
{
"type": "Image",
"url": "http://pasture-one-actor/assets/FediverseLogo.png",
"name": "name",
"imageType": "image/jpeg"
}
]
}
}
mastodon
{
"id": "115587916554379859",
"created_at": "2025-11-21T13:27:16.000Z",
"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/M4To1nqoSz4",
"url": "http://pasture-one-actor/object/M4To1nqoSz4",
"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": "115587904635725355",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-11-21T00:00:00.000Z",
"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": "2025-11-21",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115587916540940399",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/587/916/540/940/399/original/190490dd67042dc6.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/587/916/540/940/399/small/190490dd67042dc6.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/JbbM7pwJ4VU",
"published": "2025-11-21T13:27:17Z",
"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/9Sdi5xNrPRQ",
"published": "2025-11-21T13:27:17Z",
"content": "only summary",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/5c040f6b-b8e4-4d46-b12c-51b8fc1eaf0e.png",
"summary": "summary"
}
}
}
mastodon
{
"id": "115587916605088352",
"created_at": "2025-11-21T13:27:17.000Z",
"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/9Sdi5xNrPRQ",
"url": "http://pasture-one-actor/object/9Sdi5xNrPRQ",
"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": "115587904635725355",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-11-21T00:00:00.000Z",
"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": "2025-11-21",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115587916599428508",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/587/916/599/428/508/original/3d822fa52014e874.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/587/916/599/428/508/small/3d822fa52014e874.png",
"remote_url": "http://pasture-one-actor/images/5c040f6b-b8e4-4d46-b12c-51b8fc1eaf0e.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": "U1LqiW^{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": [
"http://mastodon/users/hippo",
"https://www.w3.org/ns/activitystreams#Public"
],
"id": "http://pasture-one-actor/activity/mnTEDWHQKeA",
"published": "2025-11-21T13:27:18Z",
"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/b-H_hbueWBs",
"published": "2025-11-21T13:27:18Z",
"content": "only content",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/33db188f-5b71-4ae0-b68b-91bed7c1eb77.png",
"content": "content"
}
}
}
mastodon
{
"id": "115587916664955302",
"created_at": "2025-11-21T13:27:18.000Z",
"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/b-H_hbueWBs",
"url": "http://pasture-one-actor/object/b-H_hbueWBs",
"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": "115587904635725355",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-11-21T00:00:00.000Z",
"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": "2025-11-21",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115587916658547534",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/587/916/658/547/534/original/de0a923fb43058a4.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/587/916/658/547/534/small/de0a923fb43058a4.png",
"remote_url": "http://pasture-one-actor/images/33db188f-5b71-4ae0-b68b-91bed7c1eb77.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": "U07{UEyEfQyEyEfkfQfkfQfQfQfQyEfkfQfk"
}
],
"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/oF0o7zizD8U",
"published": "2025-11-21T13:27:19Z",
"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/FHw89whQQrE",
"published": "2025-11-21T13:27:19Z",
"content": "no comment in attachment; reused image",
"attachment": [
{
"type": "Image",
"url": "http://pasture-one-actor/assets/FediverseLogo.png"
}
]
}
}
mastodon
{
"id": "115587916734328189",
"created_at": "2025-11-21T13:27:19.000Z",
"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/FHw89whQQrE",
"url": "http://pasture-one-actor/object/FHw89whQQrE",
"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": "115587904635725355",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-11-21T00:00:00.000Z",
"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,
"last_status_at": "2025-11-21",
"hide_collections": true,
"emojis": [],
"fields": []
},
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