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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. firefish, 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://gotosocial/users/cookie",
    "https://www.w3.org/ns/activitystreams#Public"
  ],
  "id": "http://pasture-one-actor/actor/smwQulQQXeI",
  "published": "2025-02-15T11:49:56Z",
  "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/actor/UAj3Ejnzc2Y",
    "published": "2025-02-15T11:49:56Z",
    "content": "no description",
    "attachment": {
      "type": "Document",
      "url": "http://pasture-one-actor/images/100.png"
    },
    "tag": [
      {
        "type": "Mention",
        "href": "http://gotosocial/users/cookie"
      }
    ]
  }
}
gotosocial
{
  "id": "01JM4Q37N0F75YZ27EZ6B1X9RH",
  "created_at": "2025-02-15T11:49:56.000Z",
  "in_reply_to_id": null,
  "in_reply_to_account_id": null,
  "sensitive": false,
  "spoiler_text": "",
  "visibility": "public",
  "language": null,
  "uri": "http://pasture-one-actor/actor/UAj3Ejnzc2Y",
  "url": "http://pasture-one-actor/actor/UAj3Ejnzc2Y",
  "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": "01JM4Q0JSSGZ5ZVQKH9ZP4S8D8",
    "username": "actor",
    "acct": "actor@pasture-one-actor",
    "display_name": "Test Actor",
    "locked": true,
    "discoverable": false,
    "bot": false,
    "created_at": "2025-02-15T11:48:29.127Z",
    "note": "",
    "url": "http://pasture-one-actor/actor",
    "avatar": "http://gotosocial/assets/default_avatars/GoToSocial_icon5.png",
    "avatar_static": "http://gotosocial/assets/default_avatars/GoToSocial_icon5.png",
    "header": "http://gotosocial/assets/default_header.png",
    "header_static": "http://gotosocial/assets/default_header.png",
    "followers_count": 0,
    "following_count": 0,
    "statuses_count": 34,
    "last_status_at": "2025-02-15T11:49:56.000Z",
    "emojis": [],
    "fields": []
  },
  "media_attachments": [
    {
      "id": "01JM4Q380ZV3Q13ZSEERQKRH67",
      "type": "image",
      "url": "http://gotosocial/fileserver/01JM4Q0JSSGZ5ZVQKH9ZP4S8D8/attachment/original/01JM4Q380ZV3Q13ZSEERQKRH67.png",
      "text_url": "http://gotosocial/fileserver/01JM4Q0JSSGZ5ZVQKH9ZP4S8D8/attachment/original/01JM4Q380ZV3Q13ZSEERQKRH67.png",
      "preview_url": "http://gotosocial/fileserver/01JM4Q0JSSGZ5ZVQKH9ZP4S8D8/attachment/small/01JM4Q380ZV3Q13ZSEERQKRH67.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": "L16KLOy;fQy;y;kBfQkBfQfQfQfQ"
    }
  ],
  "mentions": [
    {
      "id": "01D7RQJ29VBSRM705B1DQFH2BK",
      "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": [
    "http://gotosocial/users/cookie",
    "https://www.w3.org/ns/activitystreams#Public"
  ],
  "id": "http://pasture-one-actor/actor/iUPfKZ26pDE",
  "published": "2025-02-15T11:49:56Z",
  "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/actor/1DMnS_YSWk8",
    "published": "2025-02-15T11:49:56Z",
    "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": "01JM4Q37N0THJAAZX6SQZE7BET",
  "created_at": "2025-02-15T11:49:56.000Z",
  "in_reply_to_id": null,
  "in_reply_to_account_id": null,
  "sensitive": false,
  "spoiler_text": "",
  "visibility": "public",
  "language": null,
  "uri": "http://pasture-one-actor/actor/1DMnS_YSWk8",
  "url": "http://pasture-one-actor/actor/1DMnS_YSWk8",
  "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": "01JM4Q0JSSGZ5ZVQKH9ZP4S8D8",
    "username": "actor",
    "acct": "actor@pasture-one-actor",
    "display_name": "Test Actor",
    "locked": true,
    "discoverable": false,
    "bot": false,
    "created_at": "2025-02-15T11:48:29.127Z",
    "note": "",
    "url": "http://pasture-one-actor/actor",
    "avatar": "http://gotosocial/assets/default_avatars/GoToSocial_icon5.png",
    "avatar_static": "http://gotosocial/assets/default_avatars/GoToSocial_icon5.png",
    "header": "http://gotosocial/assets/default_header.png",
    "header_static": "http://gotosocial/assets/default_header.png",
    "followers_count": 0,
    "following_count": 0,
    "statuses_count": 35,
    "last_status_at": "2025-02-15T11:49:56.000Z",
    "emojis": [],
    "fields": []
  },
  "media_attachments": [
    {
      "id": "01JM4Q38PEAESJZ424Z8ANBCJ6",
      "type": "image",
      "url": "http://gotosocial/fileserver/01JM4Q0JSSGZ5ZVQKH9ZP4S8D8/attachment/original/01JM4Q38PEAESJZ424Z8ANBCJ6.png",
      "text_url": "http://gotosocial/fileserver/01JM4Q0JSSGZ5ZVQKH9ZP4S8D8/attachment/original/01JM4Q38PEAESJZ424Z8ANBCJ6.png",
      "preview_url": "http://gotosocial/fileserver/01JM4Q0JSSGZ5ZVQKH9ZP4S8D8/attachment/small/01JM4Q38PEAESJZ424Z8ANBCJ6.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": "L8Q~vw}sfQ}s}soLfQoLfQfQfQfQ"
    }
  ],
  "mentions": [
    {
      "id": "01D7RQJ29VBSRM705B1DQFH2BK",
      "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": [
    "http://gotosocial/users/cookie",
    "https://www.w3.org/ns/activitystreams#Public"
  ],
  "id": "http://pasture-one-actor/actor/ny7siP_HJYg",
  "published": "2025-02-15T11:49:57Z",
  "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/actor/4iuEtB64rJI",
    "published": "2025-02-15T11:49:57Z",
    "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": "01JM4Q38M8RBX9K3PG8ESYQWR0",
  "created_at": "2025-02-15T11:49:57.000Z",
  "in_reply_to_id": null,
  "in_reply_to_account_id": null,
  "sensitive": false,
  "spoiler_text": "",
  "visibility": "public",
  "language": null,
  "uri": "http://pasture-one-actor/actor/4iuEtB64rJI",
  "url": "http://pasture-one-actor/actor/4iuEtB64rJI",
  "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": "01JM4Q0JSSGZ5ZVQKH9ZP4S8D8",
    "username": "actor",
    "acct": "actor@pasture-one-actor",
    "display_name": "Test Actor",
    "locked": true,
    "discoverable": false,
    "bot": false,
    "created_at": "2025-02-15T11:48:29.127Z",
    "note": "",
    "url": "http://pasture-one-actor/actor",
    "avatar": "http://gotosocial/assets/default_avatars/GoToSocial_icon5.png",
    "avatar_static": "http://gotosocial/assets/default_avatars/GoToSocial_icon5.png",
    "header": "http://gotosocial/assets/default_header.png",
    "header_static": "http://gotosocial/assets/default_header.png",
    "followers_count": 0,
    "following_count": 0,
    "statuses_count": 36,
    "last_status_at": "2025-02-15T11:49:57.000Z",
    "emojis": [],
    "fields": []
  },
  "media_attachments": [
    {
      "id": "01JM4Q39BGA24VCGG9HM91H0BZ",
      "type": "image",
      "url": "http://gotosocial/fileserver/01JM4Q0JSSGZ5ZVQKH9ZP4S8D8/attachment/original/01JM4Q39BGA24VCGG9HM91H0BZ.png",
      "text_url": "http://gotosocial/fileserver/01JM4Q0JSSGZ5ZVQKH9ZP4S8D8/attachment/original/01JM4Q39BGA24VCGG9HM91H0BZ.png",
      "preview_url": "http://gotosocial/fileserver/01JM4Q0JSSGZ5ZVQKH9ZP4S8D8/attachment/small/01JM4Q39BGA24VCGG9HM91H0BZ.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": "01D7RQJ29VBSRM705B1DQFH2BK",
      "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": [
    "http://gotosocial/users/cookie",
    "https://www.w3.org/ns/activitystreams#Public"
  ],
  "id": "http://pasture-one-actor/actor/6opZtr06fHo",
  "published": "2025-02-15T11:49:58Z",
  "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/actor/u-f1iFVZ3Wc",
    "published": "2025-02-15T11:49:58Z",
    "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": "01JM4Q39KGDD191J739APEWMDW",
  "created_at": "2025-02-15T11:49:58.000Z",
  "in_reply_to_id": null,
  "in_reply_to_account_id": null,
  "sensitive": false,
  "spoiler_text": "",
  "visibility": "public",
  "language": null,
  "uri": "http://pasture-one-actor/actor/u-f1iFVZ3Wc",
  "url": "http://pasture-one-actor/actor/u-f1iFVZ3Wc",
  "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": "01JM4Q0JSSGZ5ZVQKH9ZP4S8D8",
    "username": "actor",
    "acct": "actor@pasture-one-actor",
    "display_name": "Test Actor",
    "locked": true,
    "discoverable": false,
    "bot": false,
    "created_at": "2025-02-15T11:48:29.127Z",
    "note": "",
    "url": "http://pasture-one-actor/actor",
    "avatar": "http://gotosocial/assets/default_avatars/GoToSocial_icon5.png",
    "avatar_static": "http://gotosocial/assets/default_avatars/GoToSocial_icon5.png",
    "header": "http://gotosocial/assets/default_header.png",
    "header_static": "http://gotosocial/assets/default_header.png",
    "followers_count": 0,
    "following_count": 0,
    "statuses_count": 37,
    "last_status_at": "2025-02-15T11:49:58.000Z",
    "emojis": [],
    "fields": []
  },
  "media_attachments": [
    {
      "id": "01JM4Q3A0J393JDP4YZ8XDKT5D",
      "type": "image",
      "url": "http://gotosocial/fileserver/01JM4Q0JSSGZ5ZVQKH9ZP4S8D8/attachment/original/01JM4Q3A0J393JDP4YZ8XDKT5D.png",
      "text_url": "http://gotosocial/fileserver/01JM4Q0JSSGZ5ZVQKH9ZP4S8D8/attachment/original/01JM4Q3A0J393JDP4YZ8XDKT5D.png",
      "preview_url": "http://gotosocial/fileserver/01JM4Q0JSSGZ5ZVQKH9ZP4S8D8/attachment/small/01JM4Q3A0J393JDP4YZ8XDKT5D.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": "01D7RQJ29VBSRM705B1DQFH2BK",
      "username": "cookie",
      "url": "http://gotosocial/@cookie",
      "acct": "cookie"
    }
  ],
  "tags": [],
  "emojis": [],
  "card": null,
  "poll": null
}