protodemo barcodes

What does a barcode know about you?

A barcode is text your eye cannot read. Pick one below, edit what it says, then try to wreck it with a pen. After every stroke a real barcode reader runs in your browser and tells you what it can still make out.

Pick a code

Waiting for a code
What a scanner gets
waiting for the first read

 

 

Warming up the reader.
Altered
0%
Things to try

Make it lie

PDF417 at its weakest

With error correction at 0, the license format sometimes reads back wrong instead of failing. Scatter tiny dots until the scanner text disagrees with yours.

One hole or many dots?

QR at full strength

Draw one fat blob. Start over. Scatter the same ink as dots. One of these kills the code far sooner.

Pen against eraser

black or white damage

Wreck the same spot twice, once with each tool. The QR forgives one of them far longer. Aztec takes the other side.

The three families

Linear

1D · bars in a row

The whole message repeats on every horizontal line from top to bottom, so a scanner only needs one clean slice across the middle. Erase the bottom two thirds and it reads fine. Take a thin vertical nick out of the middle and it dies.

Matrix

2D · a grid of squares

Read in both directions at once. The three big squares in a QR code's corners are finder patterns, telling the scanner where the code is and how it is turned. Reed and Solomon error correction lets a missing chunk be rebuilt from what survives.

Stacked

2D · rows piled up

Rows of a linear code stacked on top of each other, each row carrying its own start and stop markers so the scanner can find its place. PDF417 is the dense block on the back of a US driver's license.

Which codes tend to carry a person
  1. PDF417 and its smaller cousinsThe standard on the back of a US driver's license, plus loan packages and boarding passes. Holds the name, address and date of birth printed on the front.
  2. CodabarSurvives almost entirely on blood bank bags, library cards and some lab paperwork. Person-linked by construction.
  3. Code 128, Code 93, Code 39Hospital wristbands, specimen labels, prescription labels. Also a great deal of ordinary logistics, which is why they sit below Codabar.
  4. AztecBoarding passes, transit tickets, health passes.
  5. QRMostly web links, but patient portals, wifi credentials and payment handles all live here too.
  6. Data MatrixPharmacy unit dose and industrial part marking. Product data more often than personal data.
  7. ITFShipping cartons and logistics counts.
  8. UPC and EANRetail product numbers. A product number is all they are able to hold.

That ordering is the interesting part. When a code is damaged past reading, there is no way to know what it said, so the kind of code becomes the only evidence you have. Lex Cloak uses the ranking above to decide what to do with an unreadable code it finds in a PDF: the kinds that usually carry people arrive switched on and ready to redact, and the kinds that usually carry a product number arrive marked for review and switched off, for you to turn on if you know better. You can see why anything got flagged.

Every sample payload on this page is invented. No real names, licenses or record numbers.