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://misskey/users/acg1try90vrs0003"
],
"id": "http://pasture-one-actor/activity/BWC3lwfqDJg",
"published": "2025-09-09T11:49:03Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/acg1try90vrs0003"
],
"id": "http://pasture-one-actor/object/FIQmwOxi7fQ",
"published": "2025-09-09T11:49:03Z",
"content": "no description",
"attachment": {
"type": "Document",
"url": "http://pasture-one-actor/images/100.png"
}
}
}
misskey
{
"id": "acg1xrq0voex002e",
"createdAt": "2025-09-09T11:49:03.000Z",
"userId": "acg1vki1voex0003",
"user": {
"id": "acg1vki1voex0003",
"name": "Test Actor",
"username": "actor",
"host": "pasture-one-actor",
"avatarUrl": "http://misskey/identicon/actor@pasture-one-actor",
"avatarBlurhash": null,
"avatarDecorations": [],
"isBot": false,
"isCat": false,
"instance": {
"name": null,
"softwareName": null,
"softwareVersion": null,
"iconUrl": null,
"faviconUrl": null,
"themeColor": null
},
"emojis": {},
"onlineStatus": "unknown"
},
"text": "no description",
"cw": null,
"visibility": "public",
"localOnly": false,
"reactionAcceptance": null,
"renoteCount": 0,
"repliesCount": 0,
"reactionCount": 0,
"reactions": {},
"reactionEmojis": {},
"emojis": {},
"fileIds": [
"acg1xs1yvoex002d"
],
"files": [
{
"id": "acg1xs1yvoex002d",
"createdAt": "2025-09-09T11:49:03.430Z",
"name": "100.png",
"type": "image/png",
"md5": "59c1c19d259a40b046ec634bd3edda52",
"size": 0,
"isSensitive": false,
"blurhash": "e3QN#1}DfQ}DfQ}DjtfQjtfQfQfQfQfQfQ}DjtfQjtfQfQfQfQfQfQ",
"properties": {
"width": 40,
"height": 40
},
"url": "http://pasture-one-actor/images/100.png",
"thumbnailUrl": "http://pasture-one-actor/images/100.png",
"comment": null,
"folderId": null,
"folder": null,
"userId": "acg1vki1voex0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/FIQmwOxi7fQ",
"clippedCount": 0
}
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://misskey/users/acg1try90vrs0003"
],
"id": "http://pasture-one-actor/activity/H2awvaH0sUI",
"published": "2025-09-09T11:49:03Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/acg1try90vrs0003"
],
"id": "http://pasture-one-actor/object/aM0oFIhPLto",
"published": "2025-09-09T11:49:03Z",
"content": "name and summary",
"attachment": {
"type": "Document",
"url": "http://pasture-one-actor/images/100.png",
"name": "name",
"summary": "summary",
"content": "content"
}
}
}
misskey
{
"id": "acg1xrq0voex002g",
"createdAt": "2025-09-09T11:49:03.000Z",
"userId": "acg1vki1voex0003",
"user": {
"id": "acg1vki1voex0003",
"name": "Test Actor",
"username": "actor",
"host": "pasture-one-actor",
"avatarUrl": "http://misskey/identicon/actor@pasture-one-actor",
"avatarBlurhash": null,
"avatarDecorations": [],
"isBot": false,
"isCat": false,
"instance": {
"name": null,
"softwareName": null,
"softwareVersion": null,
"iconUrl": null,
"faviconUrl": null,
"themeColor": null
},
"emojis": {},
"onlineStatus": "unknown"
},
"text": "name and summary",
"cw": null,
"visibility": "public",
"localOnly": false,
"reactionAcceptance": null,
"renoteCount": 0,
"repliesCount": 0,
"reactionCount": 0,
"reactions": {},
"reactionEmojis": {},
"emojis": {},
"fileIds": [
"acg1xsjrvoex002f"
],
"files": [
{
"id": "acg1xsjrvoex002f",
"createdAt": "2025-09-09T11:49:04.071Z",
"name": "100.png",
"type": "image/png",
"md5": "5131e46ac7cf62cf4dc3d1ec51626079",
"size": 0,
"isSensitive": false,
"blurhash": "e3RQRI}DfQ}DfQ}DjtfQjtfQfQfQfQfQfQ}DjtfQjtfQfQfQfQfQfQ",
"properties": {
"width": 40,
"height": 40
},
"url": "http://pasture-one-actor/images/100.png",
"thumbnailUrl": "http://pasture-one-actor/images/100.png",
"comment": "name",
"folderId": null,
"folder": null,
"userId": "acg1vki1voex0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/aM0oFIhPLto",
"clippedCount": 0
}
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://misskey/users/acg1try90vrs0003"
],
"id": "http://pasture-one-actor/activity/RKN0wRipaKY",
"published": "2025-09-09T11:49:04Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/acg1try90vrs0003"
],
"id": "http://pasture-one-actor/object/uhylX81FoCc",
"published": "2025-09-09T11:49:04Z",
"content": "only name",
"attachment": [
{
"type": "Document",
"url": "http://pasture-one-actor/assets/FediverseLogo.png",
"name": "name",
"imageType": "image/jpeg"
}
]
}
}
misskey
{
"id": "acg1xshsvoex002i",
"createdAt": "2025-09-09T11:49:04.000Z",
"userId": "acg1vki1voex0003",
"user": {
"id": "acg1vki1voex0003",
"name": "Test Actor",
"username": "actor",
"host": "pasture-one-actor",
"avatarUrl": "http://misskey/identicon/actor@pasture-one-actor",
"avatarBlurhash": null,
"avatarDecorations": [],
"isBot": false,
"isCat": false,
"instance": {
"name": null,
"softwareName": null,
"softwareVersion": null,
"iconUrl": null,
"faviconUrl": null,
"themeColor": null
},
"emojis": {},
"onlineStatus": "unknown"
},
"text": "only name",
"cw": null,
"visibility": "public",
"localOnly": false,
"reactionAcceptance": null,
"renoteCount": 0,
"repliesCount": 0,
"reactionCount": 0,
"reactions": {},
"reactionEmojis": {},
"emojis": {},
"fileIds": [
"acg1xt4mvoex002h"
],
"files": [
{
"id": "acg1xt4mvoex002h",
"createdAt": "2025-09-09T11:49:04.822Z",
"name": "FediverseLogo.png",
"type": "image/png",
"md5": "85e7feae66363e9e200570a28b0cf20a",
"size": 0,
"isSensitive": false,
"blurhash": "eQE_?c.}4.YJM^}fi{EVw[xu9JK[M~xI-T9+TJRPX2$$E]NFo}j1tO",
"properties": {
"width": 1548,
"height": 1548
},
"url": "http://pasture-one-actor/assets/FediverseLogo.png",
"thumbnailUrl": "http://pasture-one-actor/assets/FediverseLogo.png",
"comment": "name",
"folderId": null,
"folder": null,
"userId": "acg1vki1voex0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/uhylX81FoCc",
"clippedCount": 0
}
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://misskey/users/acg1try90vrs0003"
],
"id": "http://pasture-one-actor/activity/fqhhOdlKGQ4",
"published": "2025-09-09T11:49:05Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/acg1try90vrs0003"
],
"id": "http://pasture-one-actor/object/RNaeo0pnAPA",
"published": "2025-09-09T11:49:05Z",
"content": "no comment in attachment",
"attachment": [
{
"type": "Document",
"url": "http://pasture-one-actor/assets/FediverseLogo.png"
}
]
}
}
misskey
{
"id": "acg1xt9kvoex002j",
"createdAt": "2025-09-09T11:49:05.000Z",
"userId": "acg1vki1voex0003",
"user": {
"id": "acg1vki1voex0003",
"name": "Test Actor",
"username": "actor",
"host": "pasture-one-actor",
"avatarUrl": "http://misskey/identicon/actor@pasture-one-actor",
"avatarBlurhash": null,
"avatarDecorations": [],
"isBot": false,
"isCat": false,
"instance": {
"name": null,
"softwareName": null,
"softwareVersion": null,
"iconUrl": null,
"faviconUrl": null,
"themeColor": null
},
"emojis": {},
"onlineStatus": "unknown"
},
"text": "no comment in attachment",
"cw": null,
"visibility": "public",
"localOnly": false,
"reactionAcceptance": null,
"renoteCount": 0,
"repliesCount": 0,
"reactionCount": 0,
"reactions": {},
"reactionEmojis": {},
"emojis": {},
"fileIds": [
"acg1xt4mvoex002h"
],
"files": [
{
"id": "acg1xt4mvoex002h",
"createdAt": "2025-09-09T11:49:04.822Z",
"name": "FediverseLogo.png",
"type": "image/png",
"md5": "85e7feae66363e9e200570a28b0cf20a",
"size": 0,
"isSensitive": false,
"blurhash": "eQE_?c.}4.YJM^}fi{EVw[xu9JK[M~xI-T9+TJRPX2$$E]NFo}j1tO",
"properties": {
"width": 1548,
"height": 1548
},
"url": "http://pasture-one-actor/assets/FediverseLogo.png",
"thumbnailUrl": "http://pasture-one-actor/assets/FediverseLogo.png",
"comment": "name",
"folderId": null,
"folder": null,
"userId": "acg1vki1voex0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/RNaeo0pnAPA",
"clippedCount": 0
}