Planning tamper evidence for public QR codes
A printed QR code in a public place has a weakness no encoding choice can fix: anyone can stick a different code on top of it. The attack is cheap, quiet, and hard to spot at a glance — a small sticker, placed in seconds, redirecting every future scanner to a phishing page or a payment form the owner never approved. Tamper evidence does not make that attack impossible. It makes it visible, so that the next person who looks at the code notices something is wrong before more people scan it.
Start by sorting your codes by consequence. A code that opens an information page failing is an embarrassment; a code that collects payment or login credentials failing is an incident. That sorting should drive everything: the seal, the inspection cadence, and the escalation. High-consequence codes deserve destructible materials, frequent checks, and an escalation path measured in minutes, not days. Low-consequence codes can live with a simpler spec — but they still deserve an owner and a schedule, because an unowned code is a code nobody checks.
Materials matter, and each has a trade-off. Destructible vinyl fragments when peeled, which makes removal obvious but also means weather damage can look like tampering. Void tape leaves a visible VOID pattern on the surface when lifted, which is dramatic and clear, but it needs a clean, flat surface to bond properly. Security laminates protect against weather and scuffing while showing delamination when disturbed. On glass, mounting on the inside face removes the easiest attack entirely, since a passerby cannot reach the label. On curved or rough surfaces, mount on a smooth rigid plate first; a label that peels on its own teaches staff to ignore peeling, which is exactly the signal you need them to notice.
Placement and presentation are the cheapest defences you have. A code above comfortable reach is harder to sticker. A printed frame around the code — a border, a logo, a line of text that an overlay would cover — makes a foreign sticker stand out to anyone who has seen the original. Keep a dated photograph of each installed code so inspectors can compare what they see against what should be there, rather than relying on memory. And route inspections along paths people already walk: the person who opens the building, the cleaner, the security round. A check that needs a special trip will be skipped; a check folded into an existing round gets done.
Finally, plan the response before you need it. When someone finds a tampered code, the first step is always the same: cover or remove it so nobody else scans it. Then document — photograph it, log the time and location — and notify the owner. Verify the destination before reissuing, and check neighbouring codes for the same treatment. Keep a log of every finding, because the pattern matters: weather damage clusters by location, vandalism clusters by night, and a sticker attack may cluster by campaign. A spec is only as good as the inspections and the response behind it.