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. firefish, 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/actor/o0WOLXsAC5k",
"published": "2025-07-15T10:00:19Z",
"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/actor/yHDvqDQ6gwQ",
"published": "2025-07-15T10:00:19Z",
"content": "no description",
"attachment": {
"type": "Document",
"url": "http://pasture-one-actor/images/100.png"
}
}
}
mastodon
{
"id": "114856664733761928",
"created_at": "2025-07-15T10:00:19.000Z",
"in_reply_to_id": null,
"in_reply_to_account_id": null,
"sensitive": false,
"spoiler_text": "",
"visibility": "public",
"language": null,
"uri": "http://pasture-one-actor/actor/yHDvqDQ6gwQ",
"url": "http://pasture-one-actor/actor/yHDvqDQ6gwQ",
"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": "114856658145454670",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-07-15T00:00:00.000Z",
"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": 34,
"last_status_at": "2025-07-15",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "114856664727485312",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/114/856/664/727/485/312/original/29900ecdeb88e185.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/114/856/664/727/485/312/small/29900ecdeb88e185.png",
"remote_url": "http://pasture-one-actor/images/100.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": "U0GTa{~ifQ~i~ij@fQj@fQfQfQfQ~ij@fQj@"
}
],
"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/actor/sWzpVWe4efw",
"published": "2025-07-15T10:00:20Z",
"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/actor/sfaTM_-fjBc",
"published": "2025-07-15T10:00:20Z",
"content": "text",
"attachment": {
"type": "Document",
"url": "http://pasture-one-actor/images/100.png",
"name": "name",
"summary": "summary",
"content": "content"
}
}
}
mastodon
{
"id": "114856664802304079",
"created_at": "2025-07-15T10:00:20.000Z",
"in_reply_to_id": null,
"in_reply_to_account_id": null,
"sensitive": false,
"spoiler_text": "",
"visibility": "public",
"language": null,
"uri": "http://pasture-one-actor/actor/sfaTM_-fjBc",
"url": "http://pasture-one-actor/actor/sfaTM_-fjBc",
"replies_count": 0,
"reblogs_count": 0,
"favourites_count": 0,
"edited_at": null,
"favourited": false,
"reblogged": false,
"muted": false,
"bookmarked": false,
"content": "text",
"filtered": [],
"reblog": null,
"account": {
"id": "114856658145454670",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-07-15T00:00:00.000Z",
"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": 35,
"last_status_at": "2025-07-15",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "114856664796133678",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/114/856/664/796/133/678/original/54317759181a5082.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/114/856/664/796/133/678/small/54317759181a5082.png",
"remote_url": "http://pasture-one-actor/images/100.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": "U0I3sk}=fQ}=}=j@fQj@fQfQfQfQ}=j@fQj@"
}
],
"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/actor/GrTogPh1clk",
"published": "2025-07-15T10:00:21Z",
"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/actor/dnSBsB9vhOM",
"published": "2025-07-15T10:00:21Z",
"content": "text",
"attachment": [
{
"type": "Document",
"url": "http://pasture-one-actor/assets/FediverseLogo.png",
"name": "name",
"imageType": "image/jpeg"
}
]
}
}
mastodon
{
"id": "114856664872906422",
"created_at": "2025-07-15T10:00:21.000Z",
"in_reply_to_id": null,
"in_reply_to_account_id": null,
"sensitive": false,
"spoiler_text": "",
"visibility": "public",
"language": null,
"uri": "http://pasture-one-actor/actor/dnSBsB9vhOM",
"url": "http://pasture-one-actor/actor/dnSBsB9vhOM",
"replies_count": 0,
"reblogs_count": 0,
"favourites_count": 0,
"edited_at": null,
"favourited": false,
"reblogged": false,
"muted": false,
"bookmarked": false,
"content": "text",
"filtered": [],
"reblog": null,
"account": {
"id": "114856658145454670",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-07-15T00:00:00.000Z",
"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": 36,
"last_status_at": "2025-07-15",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "114856664860271780",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/114/856/664/860/271/780/original/fe0f26687423ee38.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/114/856/664/860/271/780/small/fe0f26687423ee38.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/actor/VnZBIYKbuA4",
"published": "2025-07-15T10:00:22Z",
"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/actor/YNCm36Jy7_A",
"published": "2025-07-15T10:00:22Z",
"content": "no comment in attachment",
"attachment": [
{
"type": "Document",
"url": "http://pasture-one-actor/assets/FediverseLogo.png"
}
]
}
}
mastodon
{
"id": "114856664936172074",
"created_at": "2025-07-15T10:00:22.000Z",
"in_reply_to_id": null,
"in_reply_to_account_id": null,
"sensitive": false,
"spoiler_text": "",
"visibility": "public",
"language": null,
"uri": "http://pasture-one-actor/actor/YNCm36Jy7_A",
"url": "http://pasture-one-actor/actor/YNCm36Jy7_A",
"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",
"filtered": [],
"reblog": null,
"account": {
"id": "114856658145454670",
"username": "actor",
"acct": "actor@pasture-one-actor",
"display_name": "Test Actor",
"locked": false,
"bot": false,
"discoverable": false,
"indexable": false,
"group": false,
"created_at": "2025-07-15T00:00:00.000Z",
"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": 37,
"last_status_at": "2025-07-15",
"hide_collections": true,
"emojis": [],
"fields": []
},
"media_attachments": [
{
"id": "114856664922418236",
"type": "image",
"url": "http://localhost:2970/system/cache/media_attachments/files/114/856/664/922/418/236/original/bf87e6c8ddc4a78d.png",
"preview_url": "http://localhost:2970/system/cache/media_attachments/files/114/856/664/922/418/236/small/bf87e6c8ddc4a78d.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
}