← s2ars2ar

Certify a screenshot

Send fewer image tokens without the model reading the screenshot differently. certify compresses the image to the smallest version the target reads the same way, measures the drift with a deterministic witness (OCR here, since the image is text), and seals the result as an Assay record signed by the issuer’s key. The image is a synthetic invoice from our own test corpus.

2calls answered
2receipts re-hashed
2records verified
$0.02list price for a stranger
4,922ms end to end
pass · 2 records verified

Run 2026-10-11 05:26 UTC against api.s2ar.dev 0.1.1 · 2 calls · 4,922 ms · list price $0.02 for a stranger (these ran on the operator's key and cost nothing) · every number on this page re-derived by tools/walkthrough.py before it was written

1. One file in, a signed record out

curl -s -X POST 'https://api.s2ar.dev/v1/certify?probe=ocr' \
  -H "Authorization: Bearer $S2AR_KEY" \
  -F 'original=@invoice.png'

PASS → HTTP 200 · 969 ms · list price $0.01 · receipt sha256:4c3501f64c91f86e…

kindcompression
issuerassay
verdictisomorphic
outcomepass
replayabletrue
payload.tokens.anthropic{"provider": "anthropic", "before": 800, "after": 86, "saved": 714, "ratio": 0.8925}
payload.fidelity.drift0.0599
payload.fidelity.tolerance0.06
record_sha256f164152c1dd55564…
x-assay-recordf164152c1dd55564…
x-assay-verify/v1/verify/f164152c1dd555641a29b7fb2a297fc54c3d805114b426c3f3ea40983fd7bc1a
the answer, as JSON 
{
  "kind": "compression",
  "issuer": "assay",
  "verdict": "isomorphic",
  "outcome": "pass",
  "replayable": true,
  "payload.tokens.anthropic": {
    "provider": "anthropic",
    "before": 800,
    "after": 86,
    "saved": 714,
    "ratio": 0.8925
  },
  "payload.fidelity.drift": 0.0599,
  "payload.fidelity.tolerance": 0.06,
  "record_sha256": "f164152c1dd555641a29b7fb2a297fc54c3d805114b426c3f3ea40983fd7bc1a",
  "x-assay-record": "f164152c1dd555641a29b7fb2a297fc54c3d805114b426c3f3ea40983fd7bc1a",
  "x-assay-verify": "/v1/verify/f164152c1dd555641a29b7fb2a297fc54c3d805114b426c3f3ea40983fd7bc1a"
}

Assay badge for record f164152c1dd55564

re-derived by the generator
✓receipt sha256:4c3501f64c91f86e… re-derived: sha256 over the canonical answer, header and body agree
✓record f164152c1dd55564… fetched back from /v1/verify: sealed, signed, and signed by assay-1 (the key at /.well-known/assay.json)

2. The same image by URL, as a GET

A wallet that can only sign a URL sends image_url; the record names the image by hash, so the page shows the input beside it — the API returns the record, never pixels.

curl -s -X GET 'https://api.s2ar.dev/v1/certify?image_url=https%3A%2F%2Fs2ar.dev%2Fexamples%2Fmedia%2Finvoice.png&probe=ocr' \
  -H "Authorization: Bearer $S2AR_KEY"

PASS → HTTP 200 · 3953 ms · list price $0.01 · receipt sha256:a81e30b8ab8145c9…

the image sent, media/invoice.png
invoice.png
outcomepass
verdictisomorphic
witnesses.0.nameocr
subject.0.w1000
subject.0.h600
subject.1.w524
subject.1.h314
subject.1.bytes5966
payload.tokens.anthropic{"provider": "anthropic", "before": 800, "after": 220, "saved": 580, "ratio": 0.725}
payload.fidelity{"drift": 0.0, "tolerance": 0.05, "acuity": 1568}
record_sha256924aed0a44f0e675…
the answer, as JSON 
{
  "outcome": "pass",
  "verdict": "isomorphic",
  "witnesses.0.name": "ocr",
  "subject.0.w": 1000,
  "subject.0.h": 600,
  "subject.1.w": 524,
  "subject.1.h": 314,
  "subject.1.bytes": 5966,
  "payload.tokens.anthropic": {
    "provider": "anthropic",
    "before": 800,
    "after": 220,
    "saved": 580,
    "ratio": 0.725
  },
  "payload.fidelity": {
    "drift": 0.0,
    "tolerance": 0.05,
    "acuity": 1568
  },
  "record_sha256": "924aed0a44f0e6754350a2cb7e02c8d640dbfd01057843172ea77259aa31df00"
}

Assay badge for record 924aed0a44f0e675

re-derived by the generator
✓receipt sha256:a81e30b8ab8145c9… re-derived: sha256 over the canonical answer, header and body agree
✓record 924aed0a44f0e675… fetched back from /v1/verify: sealed, signed, and signed by assay-1 (the key at /.well-known/assay.json)
✓as the prose says: outcome = "pass" · verdict = "isomorphic"
✓the record names the image by hash: aea08f226ec7ac2a… equals sha256 of media/invoice.png

The record keeps hashes and dimensions, never pixels: anyone holding the two images can re-measure, and anyone at all can check the seal and the signature, free, at /v1/verify/<record_sha256>.

What this cannot buy

From the signed proceedings (/.well-known/proceedings.json), verbatim:

Failed calls are never charged. Nothing about a caller is kept. The rules: the charter.