Add EXIF metadata support for image attachments

[pfefferle]

Feature Request

Add support for embedding EXIF metadata in ActivityPub image attachments using the Vernissage namespace.

Background

Vernissage (a photo-focused Fediverse platform) has defined a namespace for sharing EXIF metadata in ActivityPub. This allows photo-centric applications to display camera settings, capture date, and other photographic information.

See discussion: https://mastodon.social/@mczachurski/115881787717042144

Proposed Implementation

Map WordPress image_meta fields to Vernissage EXIF properties:

WordPress field	Vernissage property	Example
created_timestamp	createDate	2024-01-01T00:00:00+00:00
shutter_speed	exposureTime	1/100
aperture	fNumber	f/2.8
focal_length	focalLength	50
iso	photographicSensitivity	400
camera	model	Canon EOS R5

Expected Output

{
  "type": "Image",
  "url": "https://example.com/image.jpg",
  "mediaType": "image/jpeg",
  "exif": {
    "createDate": "2024-01-01T00:00:00+00:00",
    "exposureTime": "1/100",
    "fNumber": "f/2.8",
    "focalLength": "50",
    "photographicSensitivity": "400",
    "model": "Canon EOS R5"
  }
}

Additional Considerations

• Add a filter (activitypub_image_exif) to allow extending EXIF data with additional fields like make, lens, or GPS coordinates
• Only include EXIF data when available (photos from cameras, not screenshots)

References

• Vernissage namespace: https://joinvernissage.org/ns
• Discussion: https://mastodon.social/@mczachurski/115881787717042144