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/7mq9Pz_8dq0",
"published": "2025-10-04T14:30:53Z",
"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/lCPamXFwpv0",
"published": "2025-10-04T14:30:53Z",
"content": "no description",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/63b0142e-14ec-4d0b-930f-be27e98d0e8a.png"
}
}
}
mastodon
{
"id": "115316375777978114",
"created_at": "2025-10-04T14:30:53.000Z",
"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/lCPamXFwpv0",
"url": "http://pasture-one-actor/object/lCPamXFwpv0",
"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": "115316364752975428",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-10-04T00:00:00.000Z",
"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": "2025-10-04",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115316375772721212",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/316/375/772/721/212/original/57c9d41fab6a2cc7.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/316/375/772/721/212/small/57c9d41fab6a2cc7.png",
"remote_url": "http://pasture-one-actor/images/63b0142e-14ec-4d0b-930f-be27e98d0e8a.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": "U1Ll[{][fQ][][jufQjufQfQfQfQ][jufQju"
}
],
"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/PuIjhaxhC4g",
"published": "2025-10-04T14:30:54Z",
"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/-cBJxnDVWJM",
"published": "2025-10-04T14:30:54Z",
"content": "name, summary and content",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/c378fc88-9dbf-4b93-98c9-4716e99cd03f.png",
"name": "name",
"summary": "summary",
"content": "content"
}
}
}
mastodon
{
"id": "115316375833000126",
"created_at": "2025-10-04T14:30:54.000Z",
"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/-cBJxnDVWJM",
"url": "http://pasture-one-actor/object/-cBJxnDVWJM",
"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": "115316364752975428",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-10-04T00:00:00.000Z",
"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": "2025-10-04",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115316375825425653",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/316/375/825/425/653/original/ceea018b139225ae.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/316/375/825/425/653/small/ceea018b139225ae.png",
"remote_url": "http://pasture-one-actor/images/c378fc88-9dbf-4b93-98c9-4716e99cd03f.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": "U1BREay+fQy+y+fjfQfjfQfQfQfQy+fjfQfj"
}
],
"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/Y36ZJ8uPXRA",
"published": "2025-10-04T14:30:54Z",
"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/5BO_SzuzHLQ",
"published": "2025-10-04T14:30:54Z",
"content": "only name",
"attachment": [
{
"type": "Image",
"url": "http://pasture-one-actor/assets/FediverseLogo.png",
"name": "name",
"imageType": "image/jpeg"
}
]
}
}
mastodon
{
"id": "115316375895442846",
"created_at": "2025-10-04T14:30:54.000Z",
"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/5BO_SzuzHLQ",
"url": "http://pasture-one-actor/object/5BO_SzuzHLQ",
"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": "115316364752975428",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-10-04T00:00:00.000Z",
"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": "2025-10-04",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115316375875818733",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/316/375/875/818/733/original/0aefa3bd1f0da214.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/316/375/875/818/733/small/0aefa3bd1f0da214.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/6rsJRyZYTBM",
"published": "2025-10-04T14:30:55Z",
"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/ikD4pthu1uA",
"published": "2025-10-04T14:30:55Z",
"content": "only summary",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/57991bf4-3563-4141-b128-091e7371c067.png",
"name": "name",
"summary": "summary",
"content": "content"
}
}
}
mastodon
{
"id": "115316375936969683",
"created_at": "2025-10-04T14:30:55.000Z",
"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/ikD4pthu1uA",
"url": "http://pasture-one-actor/object/ikD4pthu1uA",
"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": "115316364752975428",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-10-04T00:00:00.000Z",
"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": "2025-10-04",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115316375929279413",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/316/375/929/279/413/original/e5bf5a516d310cfc.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/316/375/929/279/413/small/e5bf5a516d310cfc.png",
"remote_url": "http://pasture-one-actor/images/57991bf4-3563-4141-b128-091e7371c067.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": "U1I^,X=QfQ=Q=QjufQjufQfQfQfQ=QjufQju"
}
],
"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/d7ovpXctdG0",
"published": "2025-10-04T14:30:56Z",
"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/uUr15BABo0s",
"published": "2025-10-04T14:30:56Z",
"content": "only content",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/a26b1338-a3db-4e66-bdf7-f13dd9ad620e.png",
"content": "content"
}
}
}
mastodon
{
"id": "115316375986548022",
"created_at": "2025-10-04T14:30:56.000Z",
"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/uUr15BABo0s",
"url": "http://pasture-one-actor/object/uUr15BABo0s",
"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": "115316364752975428",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-10-04T00:00:00.000Z",
"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": "2025-10-04",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115316375980261865",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/316/375/980/261/865/original/478f2054b5ef7d19.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/316/375/980/261/865/small/478f2054b5ef7d19.png",
"remote_url": "http://pasture-one-actor/images/a26b1338-a3db-4e66-bdf7-f13dd9ad620e.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": "U2R8gC}afQ}a}ajufQjufQfQfQfQ}ajufQju"
}
],
"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/buh9lDeC-QI",
"published": "2025-10-04T14:30:57Z",
"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/wL8cutE_LcA",
"published": "2025-10-04T14:30:57Z",
"content": "no comment in attachment; reused image",
"attachment": [
{
"type": "Image",
"url": "http://pasture-one-actor/assets/FediverseLogo.png"
}
]
}
}
mastodon
{
"id": "115316376047751537",
"created_at": "2025-10-04T14:30:57.000Z",
"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/wL8cutE_LcA",
"url": "http://pasture-one-actor/object/wL8cutE_LcA",
"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": "115316364752975428",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-10-04T00:00:00.000Z",
"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": "2025-10-04",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "115316376032611386",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/115/316/376/032/611/386/original/995f704551148cd7.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/115/316/376/032/611/386/small/995f704551148cd7.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
}