Add EXIF metadata support for image attachments

[pfefferle]

Fixes #2759

Proposed changes:

• Add EXIF metadata support for ActivityPub image attachments using Schema.org vocabulary as defined in FEP-ee3a.
• EXIF data is represented as an array of PropertyValue objects with @type, name, and value fields using the exifData property.
• Map WordPress image_meta fields to FEP-ee3a EXIF properties:
  • created_timestamp → DateTime (EXIF format "YYYY:MM:DD HH:MM:SS")
  • shutter_speed → ExposureTime (fraction format like "1/100")
  • aperture → FNumber (format like "f/2.8")
  • focal_length → FocalLength
  • iso → PhotographicSensitivity
  • camera → Model
• Add activitypub_image_exif filter for extending EXIF data (e.g., adding Make, LensModel, GPS coordinates)

Other information:

• Have you written new tests for your changes, if applicable?
• Implements FEP-ee3a: EXIF Data - a Fediverse Enhancement Proposal for standardizing EXIF metadata in ActivityPub

Testing instructions:

1. Create a post with an image that has EXIF metadata (a photo from a camera, not a screenshot)
2. Publish the post
3. View the ActivityPub JSON output for the post (add ?activitypub to the URL)
4. Verify the image attachment includes an exifData array with PropertyValue objects

Example expected output:

{
  "type": "Image",
  "url": "https://example.com/image.jpg",
  "mediaType": "image/jpeg",
  "exifData": [
    {
      "@type": "PropertyValue",
      "name": "DateTime",
      "value": "2024:01:01 00:00:00"
    },
    {
      "@type": "PropertyValue",
      "name": "ExposureTime",
      "value": "1/100"
    },
    {
      "@type": "PropertyValue",
      "name": "FNumber",
      "value": "f/2.8"
    },
    {
      "@type": "PropertyValue",
      "name": "FocalLength",
      "value": "50"
    },
    {
      "@type": "PropertyValue",
      "name": "PhotographicSensitivity",
      "value": "400"
    },
    {
      "@type": "PropertyValue",
      "name": "Model",
      "value": "Canon EOS R5"
    }
  ]
}

Changelog entry

• Automatically create a changelog entry from the details below.

Changelog Entry Details

Significance

• Patch
• Minor
• Major

Type

• Added - for new features
• Changed - for changes in existing functionality
• Deprecated - for soon-to-be removed features
• Removed - for now removed features
• Fixed - for any bug fixes
• Security - in case of vulnerabilities

Message

Add EXIF metadata support for image attachments (FEP-ee3a).

[Copilot]

Pull request overview

This PR adds EXIF metadata support for ActivityPub image attachments by implementing the Vernissage namespace specification. The implementation extracts WordPress image metadata and converts it to standardized EXIF properties that are included in ActivityPub JSON output for image attachments.

Changes:

• Added EXIF data extraction and formatting in the Base transformer class
• Added Vernissage namespace context to ActivityPub objects
• Added comprehensive test coverage for EXIF metadata handling

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
includes/transformer/class-base.php	Implements get_exif_data() method to extract and format EXIF metadata, and integrates it into transform_attachment()
includes/activity/class-base-object.php	Adds Vernissage namespace (photos) and EXIF context to ActivityPub JSON-LD
tests/phpunit/tests/includes/transformer/class-test-post.php	Adds five test cases covering EXIF data extraction, formatting, filtering, and integration
.github/changelog/2751-from-description	Documents the feature addition for changelog

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