Barcode

A barcode is a series of alternating dark and light stripes that are read by an optical scanner. The organization and width of the lines is determined by the bar code protocol selected. There are many different protocols but Code 39 is the most popular in the security industry. Sometimes the digits represented by the dark and light bars are also printed to allow people to read the number without an optical reader. The advantage of using bar code technology is that it is cheap and easy to generate the credential, and it can easily be applied to cards or other items. However the same affordability and simplicity makes the technology susceptible to fraud, because fake barcodes can also be created cheaply and easily, for example by photocopying real ones. One attempt to reduce fraud is to print the bar code using carbon-based ink and then cover the bar code with a dark red overlay. The bar code can then be read with an optical reader tuned to the infrared spectrum, but can not easily be copied by a copy machine. This does not address the ease with which bar code numbers can be generated from a computer using almost any printer. source : wikipedia.org