{
  "lesson": "23-watermarking-synthid-stable-signature-c2pa",
  "title": "Watermarking - SynthID, Stable Signature, C2PA",
  "questions": [
    {
      "stage": "pre",
      "question": "How does Kirchenbauer-style (SynthID-text) token watermarking embed a signal?",
      "options": [
        "By encrypting the output with a public key",
        "At each decoding step, hash the previous K tokens to partition the vocabulary into green/red sets and bias sampling toward green; detection counts green tokens via a z-score",
        "By inserting a hidden HTML comment",
        "By modifying the prompt template"
      ],
      "correct": 1,
      "explanation": ""
    },
    {
      "stage": "check",
      "question": "What is the primary limitation of text watermarks against paraphrase?",
      "options": [
        "Paraphrase only affects image watermarks",
        "They actually survive paraphrase",
        "Paraphrase strengthens the watermark",
        "Rewording or paraphrasing the text destroys the green-token statistical signal"
      ],
      "correct": 3,
      "explanation": ""
    },
    {
      "stage": "check",
      "question": "What does Stable Signature (Fernandez et al., ICCV 2023) do?",
      "options": [
        "Adds a visible watermark in the corner of the image",
        "Signs the metadata with a private key",
        "Uses C2PA to sign the image at upload",
        "Fine-tunes the latent diffusion decoder so every generated image carries a fixed embedded message detectable from the latent"
      ],
      "correct": 3,
      "explanation": ""
    },
    {
      "stage": "check",
      "question": "What does the May 2024 'Stable Signature is Unstable' result demonstrate?",
      "options": [
        "The watermark is provably unforgeable",
        "The watermark requires C2PA to function",
        "The watermark fails only on JPEG compression",
        "Post-generation fine-tuning of the decoder can remove the watermark while preserving image quality, undermining adversarial robustness"
      ],
      "correct": 3,
      "explanation": ""
    },
    {
      "stage": "post",
      "question": "How are C2PA metadata and watermarking complementary?",
      "options": [
        "C2PA replaces watermarks entirely",
        "Metadata can be stripped but carries rich provenance chain; watermarks persist through transcoding but carry few bits; layered, they provide a usable provenance story",
        "Watermarks are signed by the same keys as C2PA",
        "They are interchangeable"
      ],
      "correct": 1,
      "explanation": ""
    },
    {
      "stage": "post",
      "question": "Why is 'no SynthID signal' NOT proof of authenticity (human origin)?",
      "options": [
        "Because SynthID is closed-source",
        "Because SynthID always produces false positives on human text",
        "Because SynthID only watermarks generations from SynthID-enabled models; content from any model without SynthID is unwatermarked by default",
        "Because SynthID only works on Gemini outputs"
      ],
      "correct": 2,
      "explanation": ""
    }
  ]
}