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/ag0mqqelszbk0003"
],
"id": "http://pasture-one-actor/activity/HjhvWcpuWGI",
"published": "2025-12-08T11:37:21Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/ag0mqqelszbk0003"
],
"id": "http://pasture-one-actor/object/ynbX_gylKX0",
"published": "2025-12-08T11:37:21Z",
"content": "no description",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/774845a8-79bb-45f1-9a17-b8fd440bdb1a.png"
}
}
}
misskey
{
"id": "ag0n5e20gsyv002g",
"createdAt": "2025-12-08T11:37:21.000Z",
"userId": "ag0msgbpgsyv0003",
"user": {
"id": "ag0msgbpgsyv0003",
"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": [
"ag0n5e8ogsyv002f"
],
"files": [
{
"id": "ag0n5e8ogsyv002f",
"createdAt": "2025-12-08T11:37:21.240Z",
"name": "774845a8-79bb-45f1-9a17-b8fd440bdb1a.png",
"type": "image/png",
"md5": "4381363a10d54e34607495e2b0134524",
"size": 0,
"isSensitive": false,
"blurhash": "e06Y~[w|fQw|fQw|jtfQjtfQfQfQfQfQfQw|jtfQjtfQfQfQfQfQfQ",
"properties": {
"width": 40,
"height": 40
},
"url": "http://misskey/files/webpublic-39210f76-c16a-437d-8c8e-1f314de94dbe",
"thumbnailUrl": "http://misskey/proxy/static.webp?url=http%3A%2F%2Fpasture-one-actor%2Fimages%2F774845a8-79bb-45f1-9a17-b8fd440bdb1a.png&static=1",
"comment": null,
"folderId": null,
"folder": null,
"userId": "ag0msgbpgsyv0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/ynbX_gylKX0",
"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/ag0mqqelszbk0003"
],
"id": "http://pasture-one-actor/activity/oZ7PKpcfGxM",
"published": "2025-12-08T11:37:21Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/ag0mqqelszbk0003"
],
"id": "http://pasture-one-actor/object/9eB3Asw6x0s",
"published": "2025-12-08T11:37:21Z",
"content": "name, summary and content",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/1b7933d6-1d26-43be-9126-6c05c8767834.png",
"name": "name",
"summary": "summary",
"content": "content"
}
}
}
misskey
{
"id": "ag0n5e20gsyv002i",
"createdAt": "2025-12-08T11:37:21.000Z",
"userId": "ag0msgbpgsyv0003",
"user": {
"id": "ag0msgbpgsyv0003",
"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, summary and content",
"cw": null,
"visibility": "public",
"localOnly": false,
"reactionAcceptance": null,
"renoteCount": 0,
"repliesCount": 0,
"reactionCount": 0,
"reactions": {},
"reactionEmojis": {},
"emojis": {},
"fileIds": [
"ag0n5emvgsyv002h"
],
"files": [
{
"id": "ag0n5emvgsyv002h",
"createdAt": "2025-12-08T11:37:21.751Z",
"name": "1b7933d6-1d26-43be-9126-6c05c8767834.png",
"type": "image/png",
"md5": "44fa43d88676c588c3fd21b00dcb1335",
"size": 0,
"isSensitive": false,
"blurhash": "e31|WokJfQkJfQkJfRfQfRfQfQfQfQfQfQkJfRfQfRfQfQfQfQfQfQ",
"properties": {
"width": 40,
"height": 40
},
"url": "http://misskey/files/webpublic-5a0273db-4448-4ed8-9681-85d133c4f160",
"thumbnailUrl": "http://misskey/proxy/static.webp?url=http%3A%2F%2Fpasture-one-actor%2Fimages%2F1b7933d6-1d26-43be-9126-6c05c8767834.png&static=1",
"comment": "name",
"folderId": null,
"folder": null,
"userId": "ag0msgbpgsyv0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/9eB3Asw6x0s",
"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/ag0mqqelszbk0003"
],
"id": "http://pasture-one-actor/activity/AcDE_Kfqp1c",
"published": "2025-12-08T11:37:22Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/ag0mqqelszbk0003"
],
"id": "http://pasture-one-actor/object/REXCoFuqB4E",
"published": "2025-12-08T11:37:22Z",
"content": "only name",
"attachment": [
{
"type": "Image",
"url": "http://pasture-one-actor/assets/FediverseLogo.png",
"name": "name",
"imageType": "image/jpeg"
}
]
}
}
misskey
{
"id": "ag0n5etsgsyv002k",
"createdAt": "2025-12-08T11:37:22.000Z",
"userId": "ag0msgbpgsyv0003",
"user": {
"id": "ag0msgbpgsyv0003",
"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": [
"ag0n5f4xgsyv002j"
],
"files": [
{
"id": "ag0n5f4xgsyv002j",
"createdAt": "2025-12-08T11:37:22.401Z",
"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://misskey/files/webpublic-bfd94866-8f13-425f-bec7-fa221452c285",
"thumbnailUrl": "http://misskey/proxy/static.webp?url=http%3A%2F%2Fpasture-one-actor%2Fassets%2FFediverseLogo.png&static=1",
"comment": "name",
"folderId": null,
"folder": null,
"userId": "ag0msgbpgsyv0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/REXCoFuqB4E",
"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/ag0mqqelszbk0003"
],
"id": "http://pasture-one-actor/activity/ubfjzdhEORk",
"published": "2025-12-08T11:37:22Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/ag0mqqelszbk0003"
],
"id": "http://pasture-one-actor/object/15aoV1hatJo",
"published": "2025-12-08T11:37:22Z",
"content": "only summary",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/8cf9f762-684d-4aed-b3bd-d23a3075e432.png",
"summary": "summary"
}
}
}
misskey
{
"id": "ag0n5etsgsyv002m",
"createdAt": "2025-12-08T11:37:22.000Z",
"userId": "ag0msgbpgsyv0003",
"user": {
"id": "ag0msgbpgsyv0003",
"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 summary",
"cw": null,
"visibility": "public",
"localOnly": false,
"reactionAcceptance": null,
"renoteCount": 0,
"repliesCount": 0,
"reactionCount": 0,
"reactions": {},
"reactionEmojis": {},
"emojis": {},
"fileIds": [
"ag0n5fhpgsyv002l"
],
"files": [
{
"id": "ag0n5fhpgsyv002l",
"createdAt": "2025-12-08T11:37:22.861Z",
"name": "8cf9f762-684d-4aed-b3bd-d23a3075e432.png",
"type": "image/png",
"md5": "4bb4df4f2c756f7034973c8786a8e520",
"size": 0,
"isSensitive": false,
"blurhash": "e3KC?B??fQ??fQ??j[fQj[fQfQfQfQfQfQ??j[fQj[fQfQfQfQfQfQ",
"properties": {
"width": 40,
"height": 40
},
"url": "http://misskey/files/webpublic-a6428630-ab2a-4772-b743-e0e7e439bdbb",
"thumbnailUrl": "http://misskey/proxy/static.webp?url=http%3A%2F%2Fpasture-one-actor%2Fimages%2F8cf9f762-684d-4aed-b3bd-d23a3075e432.png&static=1",
"comment": null,
"folderId": null,
"folder": null,
"userId": "ag0msgbpgsyv0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/15aoV1hatJo",
"clippedCount": 0
}
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": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/ag0mqqelszbk0003"
],
"id": "http://pasture-one-actor/activity/4Kd-r_sCtds",
"published": "2025-12-08T11:37:23Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/ag0mqqelszbk0003"
],
"id": "http://pasture-one-actor/object/Z0YPI7V5ogk",
"published": "2025-12-08T11:37:23Z",
"content": "only content",
"attachment": {
"type": "Image",
"url": "http://pasture-one-actor/images/25f3e96a-0358-4bf4-8a3f-6751adab26ca.png",
"content": "content"
}
}
}
misskey
{
"id": "ag0n5flkgsyv002o",
"createdAt": "2025-12-08T11:37:23.000Z",
"userId": "ag0msgbpgsyv0003",
"user": {
"id": "ag0msgbpgsyv0003",
"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 content",
"cw": null,
"visibility": "public",
"localOnly": false,
"reactionAcceptance": null,
"renoteCount": 0,
"repliesCount": 0,
"reactionCount": 0,
"reactions": {},
"reactionEmojis": {},
"emojis": {},
"fileIds": [
"ag0n5fwtgsyv002n"
],
"files": [
{
"id": "ag0n5fwtgsyv002n",
"createdAt": "2025-12-08T11:37:23.405Z",
"name": "25f3e96a-0358-4bf4-8a3f-6751adab26ca.png",
"type": "image/png",
"md5": "9d4ae714720e18434af96f6c417fe29f",
"size": 0,
"isSensitive": false,
"blurhash": "e2NQsO}xfQ}xfQ}xj[fQj[fQfQfQfQfQfQ}xj[fQj[fQfQfQfQfQfQ",
"properties": {
"width": 40,
"height": 40
},
"url": "http://misskey/files/webpublic-db346e64-77ee-4c95-8f19-524cd21e6992",
"thumbnailUrl": "http://misskey/proxy/static.webp?url=http%3A%2F%2Fpasture-one-actor%2Fimages%2F25f3e96a-0358-4bf4-8a3f-6751adab26ca.png&static=1",
"comment": null,
"folderId": null,
"folder": null,
"userId": "ag0msgbpgsyv0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/Z0YPI7V5ogk",
"clippedCount": 0
}
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": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/ag0mqqelszbk0003"
],
"id": "http://pasture-one-actor/activity/ediK5RNpDoA",
"published": "2025-12-08T11:37:23Z",
"object": {
"type": "Note",
"attributedTo": "http://pasture-one-actor/actor",
"to": [
"https://www.w3.org/ns/activitystreams#Public",
"http://misskey/users/ag0mqqelszbk0003"
],
"id": "http://pasture-one-actor/object/TH74ilReVZE",
"published": "2025-12-08T11:37:23Z",
"content": "no comment in attachment; reused image",
"attachment": [
{
"type": "Image",
"url": "http://pasture-one-actor/assets/FediverseLogo.png"
}
]
}
}
misskey
{
"id": "ag0n5flkgsyv002p",
"createdAt": "2025-12-08T11:37:23.000Z",
"userId": "ag0msgbpgsyv0003",
"user": {
"id": "ag0msgbpgsyv0003",
"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; reused image",
"cw": null,
"visibility": "public",
"localOnly": false,
"reactionAcceptance": null,
"renoteCount": 0,
"repliesCount": 0,
"reactionCount": 0,
"reactions": {},
"reactionEmojis": {},
"emojis": {},
"fileIds": [
"ag0n5f4xgsyv002j"
],
"files": [
{
"id": "ag0n5f4xgsyv002j",
"createdAt": "2025-12-08T11:37:22.401Z",
"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://misskey/files/webpublic-bfd94866-8f13-425f-bec7-fa221452c285",
"thumbnailUrl": "http://misskey/proxy/static.webp?url=http%3A%2F%2Fpasture-one-actor%2Fassets%2FFediverseLogo.png&static=1",
"comment": "name",
"folderId": null,
"folder": null,
"userId": "ag0msgbpgsyv0003",
"user": null
}
],
"replyId": null,
"renoteId": null,
"uri": "http://pasture-one-actor/object/TH74ilReVZE",
"clippedCount": 0
}