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://misskey/users/ac4e509pcgy40003",
"https://www.w3.org/ns/activitystreams#Public"
],
"id": "http://pasture-one-actor/activity/i_vkDy33MAo",
"published": "2025-09-01T08:00:01Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/ac4e509pcgy40003"
],
"id": "http://pasture-one-actor/object/P7RPv9uNMsI",
"published": "2025-09-01T08:00:01Z",
"content": "no description",
"attachment": {
"type": "Document",
"url": "http://pasture-one-actor/images/100.png"
}
}
}
misskey
{
"id": "ac4e8ezs3xwh001j",
"createdAt": "2025-09-01T08:00:01.000Z",
"userId": "ac4e6lk83xwh0003",
"user": {
"id": "ac4e6lk83xwh0003",
"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": [
"ac4e8f4t3xwh001i"
],
"files": [
{
"id": "ac4e8f4t3xwh001i",
"createdAt": "2025-09-01T08:00:01.181Z",
"name": "100.png",
"type": "image/png",
"md5": "7b5b3f28f72c2d6cba0694583c62dc3f",
"size": 0,
"isSensitive": false,
"blurhash": "e258EzpMfQpMfQpMfkfQfkfQfQfQfQfQfQpMfkfQfkfQfQfQfQfQfQ",
"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": "ac4e6lk83xwh0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/P7RPv9uNMsI",
"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": [
"http://misskey/users/ac4e509pcgy40003",
"https://www.w3.org/ns/activitystreams#Public"
],
"id": "http://pasture-one-actor/activity/FvlLbIsnPlw",
"published": "2025-09-01T08:00:01Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/ac4e509pcgy40003"
],
"id": "http://pasture-one-actor/object/u1LDV-25kdo",
"published": "2025-09-01T08:00:01Z",
"content": "text",
"attachment": {
"type": "Document",
"url": "http://pasture-one-actor/images/100.png",
"name": "name",
"summary": "summary",
"content": "content"
}
}
}
misskey
{
"id": "ac4e8ezs3xwh001l",
"createdAt": "2025-09-01T08:00:01.000Z",
"userId": "ac4e6lk83xwh0003",
"user": {
"id": "ac4e6lk83xwh0003",
"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": [
"ac4e8fnm3xwh001k"
],
"files": [
{
"id": "ac4e8fnm3xwh001k",
"createdAt": "2025-09-01T08:00:01.858Z",
"name": "100.png",
"type": "image/png",
"md5": "2d8f19ceec88302ced02092eeceeb3c2",
"size": 0,
"isSensitive": false,
"blurhash": "e3KM^9?^fQ?^fQ?^j[fQj[fQfQfQfQfQfQ?^j[fQj[fQfQfQfQfQfQ",
"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": "ac4e6lk83xwh0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/u1LDV-25kdo",
"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": [
"http://misskey/users/ac4e509pcgy40003",
"https://www.w3.org/ns/activitystreams#Public"
],
"id": "http://pasture-one-actor/activity/aDzvf05jRWg",
"published": "2025-09-01T08:00:02Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/ac4e509pcgy40003"
],
"id": "http://pasture-one-actor/object/YflkYAYtfWc",
"published": "2025-09-01T08:00:02Z",
"content": "text",
"attachment": [
{
"type": "Document",
"url": "http://pasture-one-actor/assets/FediverseLogo.png",
"name": "name",
"imageType": "image/jpeg"
}
]
}
}
misskey
{
"id": "ac4e8frk3xwh001n",
"createdAt": "2025-09-01T08:00:02.000Z",
"userId": "ac4e6lk83xwh0003",
"user": {
"id": "ac4e6lk83xwh0003",
"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": [
"ac4e8g8o3xwh001m"
],
"files": [
{
"id": "ac4e8g8o3xwh001m",
"createdAt": "2025-09-01T08:00:02.616Z",
"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": "ac4e6lk83xwh0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/YflkYAYtfWc",
"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": [
"http://misskey/users/ac4e509pcgy40003",
"https://www.w3.org/ns/activitystreams#Public"
],
"id": "http://pasture-one-actor/activity/L4OxU30hCRo",
"published": "2025-09-01T08:00:03Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/ac4e509pcgy40003"
],
"id": "http://pasture-one-actor/object/NZvK4NJxIrg",
"published": "2025-09-01T08:00:03Z",
"content": "no comment in attachment",
"attachment": [
{
"type": "Document",
"url": "http://pasture-one-actor/assets/FediverseLogo.png"
}
]
}
}
misskey
{
"id": "ac4e8gjc3xwh001o",
"createdAt": "2025-09-01T08:00:03.000Z",
"userId": "ac4e6lk83xwh0003",
"user": {
"id": "ac4e6lk83xwh0003",
"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": [
"ac4e8g8o3xwh001m"
],
"files": [
{
"id": "ac4e8g8o3xwh001m",
"createdAt": "2025-09-01T08:00:02.616Z",
"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": "ac4e6lk83xwh0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/NZvK4NJxIrg",
"clippedCount": 0
}