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": [
    "https://www.w3.org/ns/activitystreams#Public",
    "http://mastodon/users/hippo"
  ],
  "id": "http://pasture_one_actor/actor/9oAzY6DMeK8",
  "object": {
    "type": "Note",
    "attributedTo": "http://pasture_one_actor/actor",
    "to": [
      "https://www.w3.org/ns/activitystreams#Public",
      "http://mastodon/users/hippo"
    ],
    "id": "http://pasture_one_actor/actor/UEuQ0T8b7a0",
    "published": "2024-03-06T16:43:36Z",
    "content": "no description",
    "attachment": {
      "type": "Document",
      "url": "http://pasture_one_actor/images/100.png"
    }
  }
}

mastodon

{
  "id": "112049744589172551",
  "created_at": "2024-03-06T16:43:36.000Z",
  "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/UEuQ0T8b7a0",
  "url": "http://pasture_one_actor/actor/UEuQ0T8b7a0",
  "replies_count": 0,
  "reblogs_count": 0,
  "favourites_count": 0,
  "edited_at": null,
  "favourited": false,
  "reblogged": false,
  "muted": false,
  "bookmarked": false,
  "content": "no description",
  "filtered": [],
  "reblog": null,
  "account": {
    "id": "112049740239482109",
    "username": "actor",
    "acct": "actor@pasture_one_actor",
    "display_name": "Test Actor",
    "locked": false,
    "bot": false,
    "discoverable": false,
    "group": false,
    "created_at": "2024-03-06T00:00:00.000Z",
    "note": "",
    "url": "http://pasture_one_actor/actor",
    "uri": "http://pasture_one_actor/actor",
    "avatar": "http://mastodon/avatars/original/missing.png",
    "avatar_static": "http://mastodon/avatars/original/missing.png",
    "header": "http://mastodon/headers/original/missing.png",
    "header_static": "http://mastodon/headers/original/missing.png",
    "followers_count": 0,
    "following_count": 0,
    "statuses_count": 29,
    "last_status_at": "2024-03-06",
    "emojis": [],
    "fields": []
  },
  "media_attachments": [
    {
      "id": "112049744584377271",
      "type": "image",
      "url": "http://localhost:2970/system/cache/media_attachments/files/112/049/744/584/377/271/original/960a72794a91529f.png",
      "preview_url": "http://localhost:2970/system/cache/media_attachments/files/112/049/744/584/377/271/small/960a72794a91529f.png",
      "remote_url": "http://pasture_one_actor/images/100.png",
      "preview_remote_url": null,
      "text_url": null,
      "meta": {
        "original": {
          "width": 40,
          "height": 40,
          "size": "40x40",
          "aspect": 1.0
        },
        "small": {
          "width": 40,
          "height": 40,
          "size": "40x40",
          "aspect": 1.0
        }
      },
      "description": null,
      "blurhash": "U4OIJh}KfQ}K}Kj[fQj[fQfQfQfQ}Kj[fQj["
    }
  ],
  "mentions": [],
  "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://mastodon/users/hippo"
  ],
  "id": "http://pasture_one_actor/actor/u6y9HdS7kYU",
  "object": {
    "type": "Note",
    "attributedTo": "http://pasture_one_actor/actor",
    "to": [
      "https://www.w3.org/ns/activitystreams#Public",
      "http://mastodon/users/hippo"
    ],
    "id": "http://pasture_one_actor/actor/88SXLPjXgU0",
    "published": "2024-03-06T16:43:39Z",
    "content": "text",
    "attachment": {
      "type": "Document",
      "url": "http://pasture_one_actor/images/100.png",
      "name": "name",
      "summary": "summary",
      "content": "content"
    }
  }
}

mastodon

{
  "id": "112049744739153136",
  "created_at": "2024-03-06T16:43:39.000Z",
  "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/88SXLPjXgU0",
  "url": "http://pasture_one_actor/actor/88SXLPjXgU0",
  "replies_count": 0,
  "reblogs_count": 0,
  "favourites_count": 0,
  "edited_at": null,
  "favourited": false,
  "reblogged": false,
  "muted": false,
  "bookmarked": false,
  "content": "text",
  "filtered": [],
  "reblog": null,
  "account": {
    "id": "112049740239482109",
    "username": "actor",
    "acct": "actor@pasture_one_actor",
    "display_name": "Test Actor",
    "locked": false,
    "bot": false,
    "discoverable": false,
    "group": false,
    "created_at": "2024-03-06T00:00:00.000Z",
    "note": "",
    "url": "http://pasture_one_actor/actor",
    "uri": "http://pasture_one_actor/actor",
    "avatar": "http://mastodon/avatars/original/missing.png",
    "avatar_static": "http://mastodon/avatars/original/missing.png",
    "header": "http://mastodon/headers/original/missing.png",
    "header_static": "http://mastodon/headers/original/missing.png",
    "followers_count": 0,
    "following_count": 0,
    "statuses_count": 30,
    "last_status_at": "2024-03-06",
    "emojis": [],
    "fields": []
  },
  "media_attachments": [
    {
      "id": "112049744736650340",
      "type": "image",
      "url": "http://localhost:2970/system/cache/media_attachments/files/112/049/744/736/650/340/original/147830d9e51eaabe.png",
      "preview_url": "http://localhost:2970/system/cache/media_attachments/files/112/049/744/736/650/340/small/147830d9e51eaabe.png",
      "remote_url": "http://pasture_one_actor/images/100.png",
      "preview_remote_url": null,
      "text_url": null,
      "meta": {
        "original": {
          "width": 40,
          "height": 40,
          "size": "40x40",
          "aspect": 1.0
        },
        "small": {
          "width": 40,
          "height": 40,
          "size": "40x40",
          "aspect": 1.0
        }
      },
      "description": "summary",
      "blurhash": "U4MWZ*}cfQ}c}cj[fQj[fQfQfQfQ}cj[fQj["
    }
  ],
  "mentions": [],
  "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://mastodon/users/hippo"
  ],
  "id": "http://pasture_one_actor/actor/fYjZRCIfgX0",
  "object": {
    "type": "Note",
    "attributedTo": "http://pasture_one_actor/actor",
    "to": [
      "https://www.w3.org/ns/activitystreams#Public",
      "http://mastodon/users/hippo"
    ],
    "id": "http://pasture_one_actor/actor/i4ZtwLd83sI",
    "published": "2024-03-06T16:43:41Z",
    "content": "text",
    "attachment": [
      {
        "type": "Document",
        "url": "http://pasture_one_actor/assets/FediverseLogo.png",
        "name": "name",
        "imageType": "image/jpeg"
      }
    ]
  }
}

mastodon

{
  "id": "112049744912902878",
  "created_at": "2024-03-06T16:43:41.000Z",
  "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/i4ZtwLd83sI",
  "url": "http://pasture_one_actor/actor/i4ZtwLd83sI",
  "replies_count": 0,
  "reblogs_count": 0,
  "favourites_count": 0,
  "edited_at": null,
  "favourited": false,
  "reblogged": false,
  "muted": false,
  "bookmarked": false,
  "content": "text",
  "filtered": [],
  "reblog": null,
  "account": {
    "id": "112049740239482109",
    "username": "actor",
    "acct": "actor@pasture_one_actor",
    "display_name": "Test Actor",
    "locked": false,
    "bot": false,
    "discoverable": false,
    "group": false,
    "created_at": "2024-03-06T00:00:00.000Z",
    "note": "",
    "url": "http://pasture_one_actor/actor",
    "uri": "http://pasture_one_actor/actor",
    "avatar": "http://mastodon/avatars/original/missing.png",
    "avatar_static": "http://mastodon/avatars/original/missing.png",
    "header": "http://mastodon/headers/original/missing.png",
    "header_static": "http://mastodon/headers/original/missing.png",
    "followers_count": 0,
    "following_count": 0,
    "statuses_count": 31,
    "last_status_at": "2024-03-06",
    "emojis": [],
    "fields": []
  },
  "media_attachments": [
    {
      "id": "112049744888085374",
      "type": "image",
      "url": "http://localhost:2970/system/cache/media_attachments/files/112/049/744/888/085/374/original/33e846a62eaa4253.png",
      "preview_url": "http://localhost:2970/system/cache/media_attachments/files/112/049/744/888/085/374/small/33e846a62eaa4253.png",
      "remote_url": "http://pasture_one_actor/assets/FediverseLogo.png",
      "preview_remote_url": null,
      "text_url": null,
      "meta": {
        "original": {
          "width": 1548,
          "height": 1548,
          "size": "1548x1548",
          "aspect": 1.0
        },
        "small": {
          "width": 480,
          "height": 480,
          "size": "480x480",
          "aspect": 1.0
        }
      },
      "description": "name",
      "blurhash": "UJC$fp*q55T?}fjFEVw[4?K[RT$l9,O?V?X2"
    }
  ],
  "mentions": [],
  "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://mastodon/users/hippo"
  ],
  "id": "http://pasture_one_actor/actor/T2ensbZ5A7s",
  "object": {
    "type": "Note",
    "attributedTo": "http://pasture_one_actor/actor",
    "to": [
      "https://www.w3.org/ns/activitystreams#Public",
      "http://mastodon/users/hippo"
    ],
    "id": "http://pasture_one_actor/actor/4Azkg-ySYXo",
    "published": "2024-03-06T16:43:43Z",
    "content": "no comment in attachment",
    "attachment": [
      {
        "type": "Document",
        "url": "http://pasture_one_actor/assets/FediverseLogo.png"
      }
    ]
  }
}

mastodon

{
  "id": "112049745062691887",
  "created_at": "2024-03-06T16:43:43.000Z",
  "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/4Azkg-ySYXo",
  "url": "http://pasture_one_actor/actor/4Azkg-ySYXo",
  "replies_count": 0,
  "reblogs_count": 0,
  "favourites_count": 0,
  "edited_at": null,
  "favourited": false,
  "reblogged": false,
  "muted": false,
  "bookmarked": false,
  "content": "no comment in attachment",
  "filtered": [],
  "reblog": null,
  "account": {
    "id": "112049740239482109",
    "username": "actor",
    "acct": "actor@pasture_one_actor",
    "display_name": "Test Actor",
    "locked": false,
    "bot": false,
    "discoverable": false,
    "group": false,
    "created_at": "2024-03-06T00:00:00.000Z",
    "note": "",
    "url": "http://pasture_one_actor/actor",
    "uri": "http://pasture_one_actor/actor",
    "avatar": "http://mastodon/avatars/original/missing.png",
    "avatar_static": "http://mastodon/avatars/original/missing.png",
    "header": "http://mastodon/headers/original/missing.png",
    "header_static": "http://mastodon/headers/original/missing.png",
    "followers_count": 0,
    "following_count": 0,
    "statuses_count": 32,
    "last_status_at": "2024-03-06",
    "emojis": [],
    "fields": []
  },
  "media_attachments": [
    {
      "id": "112049745038717510",
      "type": "image",
      "url": "http://localhost:2970/system/cache/media_attachments/files/112/049/745/038/717/510/original/9bb4c23e0f894cdc.png",
      "preview_url": "http://localhost:2970/system/cache/media_attachments/files/112/049/745/038/717/510/small/9bb4c23e0f894cdc.png",
      "remote_url": "http://pasture_one_actor/assets/FediverseLogo.png",
      "preview_remote_url": null,
      "text_url": null,
      "meta": {
        "original": {
          "width": 1548,
          "height": 1548,
          "size": "1548x1548",
          "aspect": 1.0
        },
        "small": {
          "width": 480,
          "height": 480,
          "size": "480x480",
          "aspect": 1.0
        }
      },
      "description": null,
      "blurhash": "UJC$fp*q55T?}fjFEVw[4?K[RT$l9,O?V?X2"
    }
  ],
  "mentions": [],
  "tags": [],
  "emojis": [],
  "card": null,
  "poll": null
}