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NFT System

Every valid proof of face submission produces an NFT -- a unique, non-fungible token representing the face image discovered during mining. This creates a generative art collection as a natural byproduct of the mining game.

How Mining Creates NFTs​

When a miner submits a valid proof of face transaction:

  1. The chain verifies the proof (regenerates image, runs detection, checks score)
  2. A new NFT is automatically minted to the miner's address
  3. The NFT's metadata records the mining context (proof number, difficulty, score, etc.)

No additional action is required. Submitting a valid proof is minting.

NFT Properties​

Each Facecoin NFT contains:

FaceNFTMetadata {
    token_id:       uint64       // Sequential proof number
    owner:          address      // Initially the miner, transferable
    challenge:      bytes32      // The challenge that was solved
    miner:          address      // Original miner
    nonce:          uint64       // The winning nonce
    face_score:     float64      // Detection confidence score
    face_bbox:      BoundingBox  // Face location in the image
    difficulty:     float64      // Difficulty at time of mining
    timestamp:      uint64       // When the proof was accepted
    image_seed:     bytes32      // SHA-256(challenge + miner + nonce)
}

Token ID​

Each NFT's token ID equals its sequential proof number. The first valid proof produces NFT #1, the second produces NFT #2, and so on. This creates a natural ordering tied to the history of mining activity.

Image Regeneration​

The face image is not stored on-chain -- it is regenerated on demand from the image_seed (which is SHA-256(challenge + miner + nonce)). Any node or viewer can reconstruct the exact image. This keeps on-chain data minimal while preserving the full visual artifact.

For display purposes (wallets, marketplaces, bridges), the image can be rendered as:

  • Raw greyscale: The actual image the detector saw (128x128)
  • Upscaled greyscale: Smoothed version at higher resolution
  • Colorized: Aesthetic color mapping derived from the image seed or miner address (following Myers' Facecoins approach)

NFT Operations​

Transfer​

NFTs can be transferred between addresses via a standard transfer transaction:

MsgTransferNFT {
    sender:     address
    recipient:  address
    token_id:   uint64
}

On-Chain Metadata​

All NFT metadata is stored on-chain and is fully deterministic. There are no external dependencies (no IPFS links, no centralized servers). The image itself is computable from the chain data.

The complete set of Facecoin NFTs forms a chronological gallery of machine-perceived faces. This gallery has several interesting properties:

  • Difficulty-stratified quality: NFTs mined at higher difficulty tend to have more visually striking faces, creating a natural quality gradient
  • Historically ordered: NFT #N was always mined before NFT #N+1
  • Provably unique: Each image comes from a unique challenge + miner + nonce combination; SHA-256 pre-image resistance makes duplicates virtually impossible
  • Miner-bound provenance: The original miner is permanently recorded, even after transfer

Rarity and Value​

While all Facecoin NFTs are structurally identical, several factors create natural variation in perceived value:

  • Face score: Higher scores indicate more "convincing" faces
  • Difficulty at time of mining: Higher difficulty means more computational work was required
  • Visual quality: Some faces will be more aesthetically interesting than others (subjective, but CLIP scoring could quantify this)
  • Proof number: Early proofs may have collector value (low token IDs)
  • Historical significance: Proofs at difficulty transitions, halving events, or other milestones

Bridged NFT Representation​

When bridged to Ethereum or Solana (see Bridging), the NFT metadata is mapped to the target chain's standard:

ERC-721 (Ethereum):

{
  "name": "Facecoin #1234",
  "description": "Face mined at proof 1234, difficulty 0.42, score 0.87",
  "image": "data:image/png;base64,...",
  "attributes": [
    { "trait_type": "Face Score", "value": 0.87 },
    { "trait_type": "Difficulty", "value": 0.42 },
    { "trait_type": "Proof Number", "value": 1234 },
    { "trait_type": "Timestamp", "value": 1709750400 }
  ]
}

The image is included as a base64 data URI (the 128x128 greyscale image is only ~16KB as PNG, well within on-chain limits). For the colorized version, the rendering is done at bridge time.