Large Image Inscription

When the witness discount meets digital art: a 395 KB image that nearly fills a block.

What This Demonstrates

This example illustrates the extreme case of witness data usage. A single inscription can occupy nearly an entire block’s worth of witness space — the scenario that drives the BIP-110 debate.

The Mechanics

How large inscriptions fit in blocks

The block weight limit is 4,000,000 WU. For a large image inscription:

Block weight budget:        4,000,000 WU
─────────────────────────────────────────
Typical block overhead:        ~10,000 WU  (coinbase tx, headers)
Image in witness:             ~395,000 WU  (395 KB × 1 WU/byte)
Transaction non-witness:         ~500 WU  (inputs, outputs × 4)
                              ─────────
Total for inscription:        ~405,500 WU
Remaining for other txs:    ~3,594,500 WU

A 395 KB image consumes roughly 10% of a block’s weight capacity. At the witness discount rate, this costs the same as ~100 KB of non-witness data.

The inscription structure

For a large image, the data is split across multiple pushes (max 520 bytes each):

OP_FALSE
OP_IF
  OP_PUSH "ord"
  OP_1
  OP_PUSH "image/png"
  OP_0
  OP_PUSH <bytes 0-519>       // chunk 1
  OP_PUSH <bytes 520-1039>    // chunk 2
  OP_PUSH <bytes 1040-1559>   // chunk 3
  ... (760+ pushes for a 395 KB image)
OP_ENDIF
<pubkey>
OP_CHECKSIG

Cost calculation

At 20 sat/vB (moderate fee environment):

Inscription weight:    ~395,500 WU
Virtual size:          ~395,500 / 4 = ~98,875 vB
Fee:                   98,875 × 20 = 1,977,500 sats
                       ≈ 0.0198 BTC
                       ≈ $1,980 at $100K/BTC

Without the SegWit discount, the same image would cost 4× more (~$7,920) because it would count as 395,500 × 4 = 1,582,000 WU.

Why This Is Controversial

The “abuse” argument

Critics call large inscriptions “witness abuse” because:

1. The witness discount was meant for signatures — A typical Schnorr signature is 64 bytes. A 395 KB image is ~6,172 signatures worth of data
2. It displaces financial transactions — Block space used for images can’t be used for payments
3. The data persists forever — Every full node must store this data permanently (unless pruning)

The “legitimate use” counter

Defenders argue:

1. The fee was paid at market rate — No discount beyond what the protocol provides to all witness data
2. Witness data CAN be pruned — Unlike UTXO data, old witness data is only needed for initial validation
3. Block fullness varies — Most blocks aren’t consistently full; inscriptions fill otherwise-empty space
4. The protocol allows it — If the rules permit it, restricting it requires a consensus change (soft fork)

The Numbers in Practice

During peak inscription activity (2023-2024):

Verify It Yourself

# Find a block with a large inscription (look for blocks near 4M weight)
bitcoin-cli getblock <blockhash> 1 | jq '{weight, size, nTx}'

# Decode a large transaction and check its witness size
bitcoin-cli getrawtransaction <large-inscription-txid> 2 | jq '{size, vsize, weight}'

# Compare: weight should be much less than size * 4
# (because witness data dominates and gets the discount)

You can find large inscriptions by browsing ordinals.com or checking block explorers for blocks with unusually high weight-to-transaction-count ratios.

Protocol Concepts Illustrated

• Witness discount economics — 1 WU/byte vs 4 WU/byte makes a 4× cost difference
• Block weight limits — 4M WU constrains total block content
• Data chunking — 520-byte push limit requires splitting large content
• The BIP-110 trigger — large inscriptions are the primary target of the proposal
• Fee market dynamics — inscriptions competing with payments for block space

Back to: Examples Index | Chapter 6: BIP-110 Debate