[FX] from Phenoelit gave an entertaining talk about barcode security. He covered both how the systems are implemented and how they’ve been exploited. The first example was a parking garage in Dresden that issues non unique barcodes for the unlimited passes that hotels give out. Anyone code print out an image of that particular code and park for free. German grocery stores have automated machines that refund you for your empty beer bottles. The barcode generated just states the refund amount (5 digits) that you’ll get at the register. Just stick the barcode under something like a six pack and it’ll scan even without the cashier seeing it.
Check out the video to find out more silliness involving DVD rentals, boarding passes, asset management, and SQL injection via the scanner. You can even find higher res versions in the 24C3 media archives.