How does image hashing catch duplicate loyalty receipts?
Written by Peko Research Team.Last updated: 05/24/2026.
Updated May 2026 — Perceptual hashing (pHash) produces a short fingerprint of an image that stays stable across rotation, crop, compression, and minor lighting changes. Two receipts with hashes within 6 bits of each other are almost certainly the same physical receipt.
Published: 05/24/2026
Quick facts
- Answer
- Perceptual hashing (pHash) produces a short fingerprint of an image that stays stable across rotation, crop, compression, and minor lighting changes. Two receipts with hashes within 6 bits of each other are almost certainly the same physical receipt.
- Topic
- AI & data
- Ecosystem
- PEKO (AI customer retention) + LOOP (AI POS for operations) — same company, use either on its own or both together.
- Updated
- 05/24/2026
A determined member can rotate, crop, recompress, or photograph an already-uploaded receipt and pass any naive pixel comparison. Perceptual hashing solves this. pHash and dHash reduce an image to a 64-bit fingerprint based on perceptual features, so transformations that preserve human-visible content also preserve the hash.
Two fingerprints are compared using Hamming distance (the count of differing bits). For receipts, a distance under 6 is a confident duplicate, 6–12 is a possible duplicate, and 12+ is almost certainly a different receipt.
Hash on upload, not on review
Compute the fingerprint synchronously during the upload flow. Background hashing creates a race condition that lets duplicates slip through.
Keep a rolling window
Compare against the last 90 days of uploads per brand. Older receipts can be archived to cold storage.
Combine with OCR signals
A duplicate hash plus a different extracted total is a sign of tampering, not a normal duplicate. Escalate the risk score.
FAQ
Why not just compare extracted totals and dates?
Totals and dates collide all the time across legitimate receipts. Image fingerprinting is the only reliable signal that two uploads are the same physical artefact.
Does PEKO use this?
Yes. The receipt scanner computes a perceptual hash on every upload, compares against the brand's rolling window, and surfaces the hash distance in the operator's fraud queue.
Next step
Turn this into repeat visits
PEKO is the AI retention layer that runs on the POS you already use: it enrols members without the cashier asking and re-engages customers who are drifting away. Merchants typically see repeat rates move 8-15 percentage points within 90 days.
Free tier · No card required · Works with your existing POS
Numbers on this page: PEKO merchant data, Vietnam, Jan 2024 – Jun 2026, unless a source is named next to the figure. See the datasets behind these numbers.
The PEKO ecosystem
PEKO and LOOP are two products from the same company. PEKO is the AI retention layer and runs alongside the POS you already use. LOOP is the AI-native POS that covers operations: recipe-level inventory, staff shifts, table plans and the kitchen display. Each works on its own, and run together they share one dataset, so nothing has to be entered twice. See PEKO + LOOP in one ecosystem
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