Add Assertions

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C2PA Specification Support

Truepic tools are compatible with all versions of the C2PA specification for signing. However, we recommend using the latest standards whenever possible. Please note that not all Content Credentials displays are compatible with version 2.x of the specification. This guide primarily covers assertions that comply with C2PA 2.1 and above, and references deprecated 1.4 assertions where relevant.

Assertions are key pieces of information added to a media file to provide context about the content. They are the most important details provided by the integrator—information that our tools do not automatically add. These assertions are crucial for verifying the media’s history and authenticity.

Most of our products use JSON format for adding assertions when signing a media file. You can either pass a JSON file or add assertions inline; in both cases, the JSON structure remains the same. However, the C2PA library uses raw string literals with a JSON-like structure. Be sure to convert the assertions below before using them.

Schema

The basic schema of assertions can be visualized like this:

{
  "assertions": [
    {
      "label": "{VALUE}",
      "data": {
        "{KEY}": "{VALUE}"
      }
    }
  ]
}

The top level is an object with a single assertions key that contains an array of assertion objects. Each assertion object has a label key and a data key. The label value is a string that identifies the type of assertion. The data value is an object where each entry is a key (string) and value (any type) that's specific to the type of assertion. Most assertions have more than one data point, and you're not just limited to a single assertion. The assertions array can contain multiple assertion objects of varying or the same types.

The schema you input for assertions is different from the schema shown in the validation report. While your input follows a specific format, the validation report transforms this schema to include validation results and contextual information, ensuring compliance with expected standards and providing insights into the processed data.

Enable precise redaction

Assertions included in an asset’s manifest can be removed when that asset is used as an ingredient in another manifest. The C2PA specification allows for redaction to protect privacy, enhance security, ensure relevance, and comply with regulations by selectively removing sensitive or unnecessary information.

We strongly encourage formatting multiple assertions of the same type as separate objects to enable individual redaction later. This approach allows each assertion to be redacted independently based on its label. Combining all assertions into a single object necessitates redacting the entire object, which may result in the removal of information that is desired to be retained. Separating assertions provides more precise control over what remains visible and what is redacted.

// Facilitates precise redaction
{
  "assertions": [
    {
      "label": "c2pa.metadata",
      "data": {
        "exif:DateTimeOriginal": "2023:05:11 20:36:00",
        "exif:OffsetTimeOriginal": "-04:00",
        "exif:TimeZoneName": "America/New_York"
      }
    },
    {
      "label": "c2pa.metadata",
      "data": {
        "exif:GPSLatitude": "40.748817",
        "exif:GPSLongitude": "-73.985428"
      }
    },
    {
      "label": "c2pa.metadata",
      "data": {
        "tiff:Make": "Google",
        "tiff:Model": "Pixel 5a"
      }
    }
  ]
}

// Does not facilitate precise redaction
{
  "assertions": [
    {
      "label": "c2pa.metadata",
      "data": {
        "exif:DateTimeOriginal": "2023:05:11 20:36:00",
        "exif:OffsetTimeOriginal": "-04:00",
        "exif:TimeZoneName": "America/New_York",
        "exif:GPSLatitude": "40.748817",
        "exif:GPSLongitude": "-73.985428",
        "tiff:Make": "Google",
        "tiff:Model": "Pixel 5a"
      }
    }
  ]
}

Actions assertions

An actions assertion details changes and activities affecting the asset’s content. It includes a list of actions, each describing what happened to the asset, when it happened, and possibly additional details like the software used for the action. This helps to create a complete record of the asset's history.

The most common fields used in an action assertion are:

Basic example:

{
  "assertions": [
    {
      "label": "c2pa.actions.v2",
      "data": {
        "actions": [
          {
            action: "c2pa.created",
            description: "Generated image via API",
            digitalSourceType: "http://cv.iptc.org/newscodes/digitalsourcetype/trainedAlgorithmicMedia",  
            "softwareAgent": {
              "name": "Midjourney",
              "version": "6.1"
            },
            when: "2023-05-11T20:40:00Z"  
          }
        ]
      }
    }
  ]
}

Standard actions

IPTC digitalSourceType

(Optional) Add digitalSourceType to any action.

"digitalSourceType": "http://cv.iptc.org/newscodes/digitalsourcetype/NAME"

Be sure to prepend http://cv.iptc.org/newscodes/digitalsourcetype/ to any name below. The categorization column denotes which names map to a flag in a Content Credentials display.

Metadata assertions

Including metadata in an assertion means it’s important because it’s explicitly added to the C2PA manifest and signed. This allows the data to be verified and attributed securely. Unlike standard, unprotected metadata like EXIF, which can be easily altered or ignored, this approach ensures that the metadata is both protected and consistently processed through a common format.

Prior to the 1.4 specification, there were individual assertions for each metadata standard (e.g., IPTC, EXIF). There is now a single label, stds.metadata for C2PA 1.4, or c2pa.metadata for C2PA 2.0 and above, which simplifies things and allows the spec to support other metadata standards in the future without the need to create more assertions.

Refer to Appendix A: Implementation Details for c2pa.metadata for a full list of supported and partially supported schemas. A @context object within each assertion object should always be included, to provide the namespaces for the metadata standards being specified.

Here are several assertions, which use the 2.0 label, c2pa.metadata. For signing with the 1.4 spec, use stds.metadata for the label instead.

{
  "assertions": [
    {
      "label": "c2pa.metadata",
      "data": {
        "tiff:Model": "Pixel 4",
        "tiff:Make": "Google",
        "@context": {
          "tiff": "http://ns.adobe.com/tiff/1.0/"
        }
      }
    },
    {
      "label": "c2pa.metadata",
      "data": {
        "exif:DateTimeOriginal": "2024:08:14 17:00:08",
        "@context": {
          "exif": "http://ns.adobe.com/exif/1.0/"
        }
      }
    },
    {
      "label": "c2pa.metadata",
      "data": {
        "Iptc4xmpExt:DigitalSourceType": "https://cv.iptc.org/newscodes/digitalsourcetype/digitalCapture",
        "@context": {
          "Iptc4xmpExt": "http://iptc.org/std/Iptc4xmpExt/2008-02-29/"
        }
      }
    },
    {
      "label": "c2pa.metadata",
      "data": {
        "exif:GPSLatitude": "40.748817",
        "exif:GPSLongitude": "-73.985428",
        "@context": {
          "exif": "http://ns.adobe.com/exif/1.0/"
        }
      }
    }
  ]
}

Custom assertions

Custom assertions allow you to include additional metadata or information that isn’t covered by the standard C2PA assertions. They can be useful for capturing specific details relevant to your application or use case, and for including proprietary or organization-specific information in the content credentials, such as custom tags, identifiers, or unique data formats. However, custom assertions are not validated against the C2PA specification and are not typically viewable in Content Credentials displays.

We recommend using labels in reverse domain name notation, such as com.truepic.libc2pa, or start with the organization’s name, like truepic.metadata.

{
  "assertions": [
    {
      "label": "truepic.custom",
      "data": {
        "photographer": "Joe Smith",
        "campaign_id": "1234567"
      }
    }
  ]
}

Creative work assertions

❗️

Deprecated

This assertion is deprecated in C2PA 1.4 and unsupported in 2.0+ and may not be viewable in future Content Credentials displays.

Schema.org's CreativeWork metadata standard allows a signer to include creative credits, such as naming individuals or organizations as creators, publishers, and more. However, the C2PA specification has evolved to exclude this type of opt-in, identity-based data because it is self-disclosed rather than programmatically collected by the signing system. As a result, we advise new implementers of our signing tools to avoid using this assertion.

{
  "assertions": [
    {
      "label": "stds.schema-org.CreativeWork",
      "data": {
        "@context": "https://schema.org",
        "@type": "CreativeWork",
        "author": [ // replace with other role
          {
            "@type": "Person", // "Organization" also supported
            "name": "Joe Demo"
          }
        ]
      }
    }
  ]
}

The full list of CreativeWork supported roles is: accountablePerson, author, character, contributor, copyrightHolder, creator, editor, funder, maintainer, producer, provider, publisher, publisherImprint, sdPublisher, sourceOrganization, sponsor, translator