How do barcodes work?
Answer from Indian Barcode Corporation
Different combinations of bars and spaces are used to encode characters into bar codes. Differences in light and dark and the width of the elements are the variables used for encoding. The bar code reader illuminates the symbol and measures the amount of light that is reflected back. The reader determines the pattern of light and dark or wide and narrow, then compares it to the encoding table for that type of bar code (called a symbology) and decodes the symbol.