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/acbvxoc67a2y0003"
],
"id": "http://pasture-one-actor/activity/egYJ-C39yUY",
"published": "2025-09-06T13:52:55Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/acbvxoc67a2y0003"
],
"id": "http://pasture-one-actor/object/H6xupN8A1UM",
"published": "2025-09-06T13:52:55Z",
"content": "no description",
"attachment": {
"type": "Document",
"url": "http://pasture-one-actor/images/100.png"
}
}
}
misskey
{
"id": "acbw1iagnd1t002e",
"createdAt": "2025-09-06T13:52:55.000Z",
"userId": "acbvz9wond1t0003",
"user": {
"id": "acbvz9wond1t0003",
"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": [
"acbw1j0pnd1t002d"
],
"files": [
{
"id": "acbw1j0pnd1t002d",
"createdAt": "2025-09-06T13:52:55.945Z",
"name": "100.png",
"type": "image/png",
"md5": "652d596d2c2243e4824a59e63c9140ca",
"size": 0,
"isSensitive": false,
"blurhash": "e2MdS6|$fQ|$fQ|$jufQjufQfQfQfQfQfQ|$jufQjufQfQfQfQfQfQ",
"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": "acbvz9wond1t0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/H6xupN8A1UM",
"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/acbvxoc67a2y0003"
],
"id": "http://pasture-one-actor/activity/QYNaKXcyT_8",
"published": "2025-09-06T13:52:56Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/acbvxoc67a2y0003"
],
"id": "http://pasture-one-actor/object/JuPM1o7VZ3w",
"published": "2025-09-06T13:52:56Z",
"content": "text",
"attachment": {
"type": "Document",
"url": "http://pasture-one-actor/images/100.png",
"name": "name",
"summary": "summary",
"content": "content"
}
}
}
misskey
{
"id": "acbw1j28nd1t002g",
"createdAt": "2025-09-06T13:52:56.000Z",
"userId": "acbvz9wond1t0003",
"user": {
"id": "acbvz9wond1t0003",
"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": "text",
"cw": null,
"visibility": "public",
"localOnly": false,
"reactionAcceptance": null,
"renoteCount": 0,
"repliesCount": 0,
"reactionCount": 0,
"reactions": {},
"reactionEmojis": {},
"emojis": {},
"fileIds": [
"acbw1jk2nd1t002f"
],
"files": [
{
"id": "acbw1jk2nd1t002f",
"createdAt": "2025-09-06T13:52:56.642Z",
"name": "100.png",
"type": "image/png",
"md5": "86a34a5a5644b8df1e3d9ae73fe7d89f",
"size": 0,
"isSensitive": false,
"blurhash": "e25]tUp{fQp{fQp{fkfQfkfQfQfQfQfQfQp{fkfQfkfQfQfQfQfQfQ",
"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": "acbvz9wond1t0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/JuPM1o7VZ3w",
"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/acbvxoc67a2y0003"
],
"id": "http://pasture-one-actor/activity/lgMvmP1fbGc",
"published": "2025-09-06T13:52:57Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/acbvxoc67a2y0003"
],
"id": "http://pasture-one-actor/object/1QdWQBSaNZo",
"published": "2025-09-06T13:52:57Z",
"content": "text",
"attachment": [
{
"type": "Document",
"url": "http://pasture-one-actor/assets/FediverseLogo.png",
"name": "name",
"imageType": "image/jpeg"
}
]
}
}
misskey
{
"id": "acbw1ju0nd1t002i",
"createdAt": "2025-09-06T13:52:57.000Z",
"userId": "acbvz9wond1t0003",
"user": {
"id": "acbvz9wond1t0003",
"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": "text",
"cw": null,
"visibility": "public",
"localOnly": false,
"reactionAcceptance": null,
"renoteCount": 0,
"repliesCount": 0,
"reactionCount": 0,
"reactions": {},
"reactionEmojis": {},
"emojis": {},
"fileIds": [
"acbw1k45nd1t002h"
],
"files": [
{
"id": "acbw1k45nd1t002h",
"createdAt": "2025-09-06T13:52:57.365Z",
"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": "acbvz9wond1t0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/1QdWQBSaNZo",
"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/acbvxoc67a2y0003"
],
"id": "http://pasture-one-actor/activity/ftpqzZZuTXs",
"published": "2025-09-06T13:52:57Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/acbvxoc67a2y0003"
],
"id": "http://pasture-one-actor/object/WewDsOzjXvs",
"published": "2025-09-06T13:52:57Z",
"content": "no comment in attachment",
"attachment": [
{
"type": "Document",
"url": "http://pasture-one-actor/assets/FediverseLogo.png"
}
]
}
}
misskey
{
"id": "acbw1ju0nd1t002j",
"createdAt": "2025-09-06T13:52:57.000Z",
"userId": "acbvz9wond1t0003",
"user": {
"id": "acbvz9wond1t0003",
"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": [
"acbw1k45nd1t002h"
],
"files": [
{
"id": "acbw1k45nd1t002h",
"createdAt": "2025-09-06T13:52:57.365Z",
"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": "acbvz9wond1t0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/WewDsOzjXvs",
"clippedCount": 0
}