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://gotosocial/users/cookie"
  ],
  "id": "http://pasture-one-actor/activity/pzONif68gDw",
  "published": "2025-09-01T16:40:24Z",
  "object": {
    "type": "Note",
    "attributedTo": "http://pasture-one-actor/actor",
    "to": [
      "https://www.w3.org/ns/activitystreams#Public",
      "http://gotosocial/users/cookie"
    ],
    "id": "http://pasture-one-actor/object/ryW3iG9w2zM",
    "published": "2025-09-01T16:40:24Z",
    "content": "no description",
    "attachment": {
      "type": "Document",
      "url": "http://pasture-one-actor/images/100.png"
    },
    "tag": [
      {
        "type": "Mention",
        "href": "http://gotosocial/users/cookie"
      }
    ]
  }
}

gotosocial

{
  "id": "01K432DD608PVKAE7CFGHRASFZ",
  "created_at": "2025-09-01T16:40:24.000Z",
  "in_reply_to_id": null,
  "in_reply_to_account_id": null,
  "sensitive": false,
  "spoiler_text": "",
  "visibility": "public",
  "language": null,
  "uri": "http://pasture-one-actor/object/ryW3iG9w2zM",
  "url": "http://pasture-one-actor/object/ryW3iG9w2zM",
  "replies_count": 0,
  "reblogs_count": 0,
  "favourites_count": 0,
  "favourited": false,
  "reblogged": false,
  "muted": false,
  "bookmarked": false,
  "pinned": false,
  "content": "no description",
  "reblog": null,
  "account": {
    "id": "01K432AKHKDTGSPQWT577GVG51",
    "username": "actor",
    "acct": "actor@pasture-one-actor",
    "display_name": "Test Actor",
    "locked": true,
    "discoverable": false,
    "bot": false,
    "created_at": "2025-09-01T16:38:52.221Z",
    "note": "",
    "url": "http://pasture-one-actor/actor",
    "avatar": "http://gotosocial/assets/default_avatars/GoToSocial_icon3.png",
    "avatar_static": "http://gotosocial/assets/default_avatars/GoToSocial_icon3.png",
    "header": "http://gotosocial/assets/default_header.png",
    "header_static": "http://gotosocial/assets/default_header.png",
    "followers_count": 0,
    "following_count": 0,
    "statuses_count": 46,
    "last_status_at": "2025-09-01T16:40:24.000Z",
    "emojis": [],
    "fields": []
  },
  "media_attachments": [
    {
      "id": "01K432DDNB7RRMV5K732YWWRXZ",
      "type": "image",
      "url": "http://gotosocial/fileserver/01K432AKHKDTGSPQWT577GVG51/attachment/original/01K432DDNB7RRMV5K732YWWRXZ.png",
      "text_url": "http://gotosocial/fileserver/01K432AKHKDTGSPQWT577GVG51/attachment/original/01K432DDNB7RRMV5K732YWWRXZ.png",
      "preview_url": "http://gotosocial/fileserver/01K432AKHKDTGSPQWT577GVG51/attachment/small/01K432DDNB7RRMV5K732YWWRXZ.jpg",
      "remote_url": "http://pasture-one-actor/images/100.png",
      "preview_remote_url": null,
      "meta": {
        "original": {
          "width": 40,
          "height": 40,
          "size": "40x40",
          "aspect": 1
        },
        "small": {
          "width": 40,
          "height": 40,
          "size": "40x40",
          "aspect": 1
        },
        "focus": {
          "x": 0,
          "y": 0
        }
      },
      "description": null,
      "blurhash": "L5GKn}.efQ.e.ekAfQkAfQfQfQfQ"
    }
  ],
  "mentions": [
    {
      "id": "01Q27C6HW8VQDC6CMBY9ATZV0P",
      "username": "cookie",
      "url": "http://gotosocial/@cookie",
      "acct": "cookie"
    }
  ],
  "tags": [],
  "emojis": [],
  "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": [
    "https://www.w3.org/ns/activitystreams#Public",
    "http://gotosocial/users/cookie"
  ],
  "id": "http://pasture-one-actor/activity/QmPVdx71gQY",
  "published": "2025-09-01T16:40:25Z",
  "object": {
    "type": "Note",
    "attributedTo": "http://pasture-one-actor/actor",
    "to": [
      "https://www.w3.org/ns/activitystreams#Public",
      "http://gotosocial/users/cookie"
    ],
    "id": "http://pasture-one-actor/object/We4ylZ0kgYw",
    "published": "2025-09-01T16:40:25Z",
    "content": "text",
    "attachment": {
      "type": "Document",
      "url": "http://pasture-one-actor/images/100.png",
      "name": "name",
      "summary": "summary",
      "content": "content"
    },
    "tag": [
      {
        "type": "Mention",
        "href": "http://gotosocial/users/cookie"
      }
    ]
  }
}

gotosocial

{
  "id": "01K432DE58SFKVBZWPY7HG1TT4",
  "created_at": "2025-09-01T16:40:25.000Z",
  "in_reply_to_id": null,
  "in_reply_to_account_id": null,
  "sensitive": false,
  "spoiler_text": "",
  "visibility": "public",
  "language": null,
  "uri": "http://pasture-one-actor/object/We4ylZ0kgYw",
  "url": "http://pasture-one-actor/object/We4ylZ0kgYw",
  "replies_count": 0,
  "reblogs_count": 0,
  "favourites_count": 0,
  "favourited": false,
  "reblogged": false,
  "muted": false,
  "bookmarked": false,
  "pinned": false,
  "content": "text",
  "reblog": null,
  "account": {
    "id": "01K432AKHKDTGSPQWT577GVG51",
    "username": "actor",
    "acct": "actor@pasture-one-actor",
    "display_name": "Test Actor",
    "locked": true,
    "discoverable": false,
    "bot": false,
    "created_at": "2025-09-01T16:38:52.221Z",
    "note": "",
    "url": "http://pasture-one-actor/actor",
    "avatar": "http://gotosocial/assets/default_avatars/GoToSocial_icon3.png",
    "avatar_static": "http://gotosocial/assets/default_avatars/GoToSocial_icon3.png",
    "header": "http://gotosocial/assets/default_header.png",
    "header_static": "http://gotosocial/assets/default_header.png",
    "followers_count": 0,
    "following_count": 0,
    "statuses_count": 47,
    "last_status_at": "2025-09-01T16:40:25.000Z",
    "emojis": [],
    "fields": []
  },
  "media_attachments": [
    {
      "id": "01K432DE7H3K1TWDKC3SWJRTVE",
      "type": "image",
      "url": "http://gotosocial/fileserver/01K432AKHKDTGSPQWT577GVG51/attachment/original/01K432DE7H3K1TWDKC3SWJRTVE.png",
      "text_url": "http://gotosocial/fileserver/01K432AKHKDTGSPQWT577GVG51/attachment/original/01K432DE7H3K1TWDKC3SWJRTVE.png",
      "preview_url": "http://gotosocial/fileserver/01K432AKHKDTGSPQWT577GVG51/attachment/small/01K432DE7H3K1TWDKC3SWJRTVE.jpg",
      "remote_url": "http://pasture-one-actor/images/100.png",
      "preview_remote_url": null,
      "meta": {
        "original": {
          "width": 40,
          "height": 40,
          "size": "40x40",
          "aspect": 1
        },
        "small": {
          "width": 40,
          "height": 40,
          "size": "40x40",
          "aspect": 1
        },
        "focus": {
          "x": 0,
          "y": 0
        }
      },
      "description": "summary",
      "blurhash": "L3J_|2|yfQ|y|yo2fQo2fQfQfQfQ"
    }
  ],
  "mentions": [
    {
      "id": "01Q27C6HW8VQDC6CMBY9ATZV0P",
      "username": "cookie",
      "url": "http://gotosocial/@cookie",
      "acct": "cookie"
    }
  ],
  "tags": [],
  "emojis": [],
  "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": [
    "https://www.w3.org/ns/activitystreams#Public",
    "http://gotosocial/users/cookie"
  ],
  "id": "http://pasture-one-actor/activity/rab6esHvVZ0",
  "published": "2025-09-01T16:40:25Z",
  "object": {
    "type": "Note",
    "attributedTo": "http://pasture-one-actor/actor",
    "to": [
      "https://www.w3.org/ns/activitystreams#Public",
      "http://gotosocial/users/cookie"
    ],
    "id": "http://pasture-one-actor/object/SSIEc4012ko",
    "published": "2025-09-01T16:40:25Z",
    "content": "text",
    "attachment": [
      {
        "type": "Document",
        "url": "http://pasture-one-actor/assets/FediverseLogo.png",
        "name": "name",
        "imageType": "image/jpeg"
      }
    ],
    "tag": [
      {
        "type": "Mention",
        "href": "http://gotosocial/users/cookie"
      }
    ]
  }
}

gotosocial

{
  "id": "01K432DE58BSFNY4X8WPQ8Q48B",
  "created_at": "2025-09-01T16:40:25.000Z",
  "in_reply_to_id": null,
  "in_reply_to_account_id": null,
  "sensitive": false,
  "spoiler_text": "",
  "visibility": "public",
  "language": null,
  "uri": "http://pasture-one-actor/object/SSIEc4012ko",
  "url": "http://pasture-one-actor/object/SSIEc4012ko",
  "replies_count": 0,
  "reblogs_count": 0,
  "favourites_count": 0,
  "favourited": false,
  "reblogged": false,
  "muted": false,
  "bookmarked": false,
  "pinned": false,
  "content": "text",
  "reblog": null,
  "account": {
    "id": "01K432AKHKDTGSPQWT577GVG51",
    "username": "actor",
    "acct": "actor@pasture-one-actor",
    "display_name": "Test Actor",
    "locked": true,
    "discoverable": false,
    "bot": false,
    "created_at": "2025-09-01T16:38:52.221Z",
    "note": "",
    "url": "http://pasture-one-actor/actor",
    "avatar": "http://gotosocial/assets/default_avatars/GoToSocial_icon3.png",
    "avatar_static": "http://gotosocial/assets/default_avatars/GoToSocial_icon3.png",
    "header": "http://gotosocial/assets/default_header.png",
    "header_static": "http://gotosocial/assets/default_header.png",
    "followers_count": 0,
    "following_count": 0,
    "statuses_count": 48,
    "last_status_at": "2025-09-01T16:40:25.000Z",
    "emojis": [],
    "fields": []
  },
  "media_attachments": [
    {
      "id": "01K432DESGTYEAM95TX9YW5AN3",
      "type": "image",
      "url": "http://gotosocial/fileserver/01K432AKHKDTGSPQWT577GVG51/attachment/original/01K432DESGTYEAM95TX9YW5AN3.png",
      "text_url": "http://gotosocial/fileserver/01K432AKHKDTGSPQWT577GVG51/attachment/original/01K432DESGTYEAM95TX9YW5AN3.png",
      "preview_url": "http://gotosocial/fileserver/01K432AKHKDTGSPQWT577GVG51/attachment/small/01K432DESGTYEAM95TX9YW5AN3.jpg",
      "remote_url": "http://pasture-one-actor/assets/FediverseLogo.png",
      "preview_remote_url": null,
      "meta": {
        "original": {
          "width": 1548,
          "height": 1548,
          "size": "1548x1548",
          "aspect": 1
        },
        "small": {
          "width": 512,
          "height": 512,
          "size": "512x512",
          "aspect": 1
        },
        "focus": {
          "x": 0,
          "y": 0
        }
      },
      "description": "name",
      "blurhash": "LIB{x~.}9Fcn}gnOEUxBDlK[N1wi"
    }
  ],
  "mentions": [
    {
      "id": "01Q27C6HW8VQDC6CMBY9ATZV0P",
      "username": "cookie",
      "url": "http://gotosocial/@cookie",
      "acct": "cookie"
    }
  ],
  "tags": [],
  "emojis": [],
  "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": [
    "https://www.w3.org/ns/activitystreams#Public",
    "http://gotosocial/users/cookie"
  ],
  "id": "http://pasture-one-actor/activity/PRwavydU55I",
  "published": "2025-09-01T16:40:26Z",
  "object": {
    "type": "Note",
    "attributedTo": "http://pasture-one-actor/actor",
    "to": [
      "https://www.w3.org/ns/activitystreams#Public",
      "http://gotosocial/users/cookie"
    ],
    "id": "http://pasture-one-actor/object/-eoQo16hTMI",
    "published": "2025-09-01T16:40:26Z",
    "content": "no comment in attachment",
    "attachment": [
      {
        "type": "Document",
        "url": "http://pasture-one-actor/assets/FediverseLogo.png"
      }
    ],
    "tag": [
      {
        "type": "Mention",
        "href": "http://gotosocial/users/cookie"
      }
    ]
  }
}

gotosocial

{
  "id": "01K432DF4GHG5Z903YYRVE5MTG",
  "created_at": "2025-09-01T16:40:26.000Z",
  "in_reply_to_id": null,
  "in_reply_to_account_id": null,
  "sensitive": false,
  "spoiler_text": "",
  "visibility": "public",
  "language": null,
  "uri": "http://pasture-one-actor/object/-eoQo16hTMI",
  "url": "http://pasture-one-actor/object/-eoQo16hTMI",
  "replies_count": 0,
  "reblogs_count": 0,
  "favourites_count": 0,
  "favourited": false,
  "reblogged": false,
  "muted": false,
  "bookmarked": false,
  "pinned": false,
  "content": "no comment in attachment",
  "reblog": null,
  "account": {
    "id": "01K432AKHKDTGSPQWT577GVG51",
    "username": "actor",
    "acct": "actor@pasture-one-actor",
    "display_name": "Test Actor",
    "locked": true,
    "discoverable": false,
    "bot": false,
    "created_at": "2025-09-01T16:38:52.221Z",
    "note": "",
    "url": "http://pasture-one-actor/actor",
    "avatar": "http://gotosocial/assets/default_avatars/GoToSocial_icon3.png",
    "avatar_static": "http://gotosocial/assets/default_avatars/GoToSocial_icon3.png",
    "header": "http://gotosocial/assets/default_header.png",
    "header_static": "http://gotosocial/assets/default_header.png",
    "followers_count": 0,
    "following_count": 0,
    "statuses_count": 49,
    "last_status_at": "2025-09-01T16:40:26.000Z",
    "emojis": [],
    "fields": []
  },
  "media_attachments": [
    {
      "id": "01K432DFBQYDQCRMRV5EP2YSZX",
      "type": "image",
      "url": "http://gotosocial/fileserver/01K432AKHKDTGSPQWT577GVG51/attachment/original/01K432DFBQYDQCRMRV5EP2YSZX.png",
      "text_url": "http://gotosocial/fileserver/01K432AKHKDTGSPQWT577GVG51/attachment/original/01K432DFBQYDQCRMRV5EP2YSZX.png",
      "preview_url": "http://gotosocial/fileserver/01K432AKHKDTGSPQWT577GVG51/attachment/small/01K432DFBQYDQCRMRV5EP2YSZX.jpg",
      "remote_url": "http://pasture-one-actor/assets/FediverseLogo.png",
      "preview_remote_url": null,
      "meta": {
        "original": {
          "width": 1548,
          "height": 1548,
          "size": "1548x1548",
          "aspect": 1
        },
        "small": {
          "width": 512,
          "height": 512,
          "size": "512x512",
          "aspect": 1
        },
        "focus": {
          "x": 0,
          "y": 0
        }
      },
      "description": null,
      "blurhash": "LIB{x~.}9Fcn}gnOEUxBDlK[N1wi"
    }
  ],
  "mentions": [
    {
      "id": "01Q27C6HW8VQDC6CMBY9ATZV0P",
      "username": "cookie",
      "url": "http://gotosocial/@cookie",
      "acct": "cookie"
    }
  ],
  "tags": [],
  "emojis": [],
  "card": null,
  "poll": null
}