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Python example code

The examples directory contains some small examples of using the Python library. The examples use asset files from the tests/fixtures directory, save the resulting signed assets to the temporary output directory, and display manifest store data and other output to the console.

Signing and verifying assets​

The examples/sign.py script shows how to sign an asset with a C2PA manifest and verify the asset.

The examples/sign.py script shows how to sign an asset with a C2PA manifest and verify it using a callback signer. Callback signers let you define signing logic, for example where to load keys from.

The examples/sign_info.py script shows how to sign an asset with a C2PA manifest and verify it using a "default" signer created with the needed signer information.

These statements create a builder object with the specified manifest JSON (omitted in the snippet below), call builder.sign() to sign and attach the manifest to the source file, tests/fixtures/C.jpg, and save the signed asset to the output file, output/C_signed.jpg:

manifest_definition = {
  // ... JSON omitted here
}

builder = c2pa.Builder(manifest_definition)

with open(fixtures_dir + "C.jpg", "rb") as source:
    with open(output_dir + "C_signed.jpg", "wb") as dest:
        result = builder.sign(signer, "image/jpeg", source, dest)

Then these statements read and verify the signed asset:

print("\nReading signed image metadata:")
with open(output_dir + "C_signed.jpg", "rb") as file:
    reader = c2pa.Reader("image/jpeg", file)
    print(reader.json())

Adding a "do not train" assertion​

The examples/training.py script shows how to add a "do not train" assertion to an asset, then verify the asset and display to the console whether its manifest indicates ML training is allowed.

These statements sign the asset using a stream:

    with open(testFile, "rb") as source_file:
        with open(testOutputFile, "wb") as dest_file:
            result = builder.sign(signer, "image/jpeg", source_file, dest_file)

These statements verify the asset and check its attached manifest for a "do not train" assertion:

allowed = True # opt out model, assume training is ok if the assertion doesn't exist
try:
    # Create reader using the current API
    reader = c2pa.Reader(testOutputFile)
    manifest_store = json.loads(reader.json())

    manifest = manifest_store["manifests"][manifest_store["active_manifest"]]
    for assertion in manifest["assertions"]:
        if assertion["label"] == "c2pa.training-mining":
            if getitem(assertion, ("data","entries","c2pa.ai_training","use")) == "notAllowed":
                allowed = False

    # get the ingredient thumbnail and save it to a file using resource_to_stream
    uri = getitem(manifest,("ingredients", 0, "thumbnail", "identifier"))
    with open(output_dir + "thumbnail_v2.jpg", "wb") as thumbnail_output:
        reader.resource_to_stream(uri, thumbnail_output)

except Exception as err:
    sys.exit(err)

Running the examples​

To run the examples, make sure you have the c2pa-python package installed (pip install c2pa-python) and you're in the root directory of the project. We recommend working using virtual environments (venv). Then run the examples as shown below.

Run the "do not train" assertion example:

python examples/training.py

Run the callback signing and verification example​

In this example, a callback signer is the signer:

python examples/sign.py

Run the signing and verification example​

In this example, SignerInfo creates a Signer object that signs the manifest.

python examples/sign_info.py