A barcode (also bar code) is a machine-readable representation of information in a visual format on a surface. Originally barcodes stored data in the widths and spacings of printed parallel lines, but today they also come in patterns of dots, concentric circles, and hidden in images. Barcodes can be read by optical scanners called barcode readers or scanned from an image by special software. Barcodes are widely used to implement Auto ID Data Capture (AIDC) systems that improve the speed and accuracy of computer data entry.

Barcodes (and other machine readable tags like RFID) are used wherever physical objects need to be tagged with information that is to be processed by computers. Instead of typing strings of data into a terminal, the operator only has to display the code to a barcode reader. They also work well in fully automated environments, such as baggage routing at airports.

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