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Magnetic Ink Character Recognition, or MICR, is a special kind of optical character recognition technology that was adopted mainly by the U.S banking industry to facilitate the processing of checks. Almost all U.S. checks include MICR characters at the bottom of the paper in a font known as E-13B.

The general problem of character recognition is limited in its usefulness to the degree of the accuracy of the recognition. Through the use of specially designed characters and ink with a magnetic signature, the error rate for scanning the numbers at the bottom of a typical check is smaller than with usual OCR systems. The letters are read with a device similar in nature to the head of an audio tape recorder. The reliability of MICR recognition is higher than when processed by hand, and is therefore highly useful in its domain.

MICR was developed in a pioneering project by Bank of America, leading to the development of one of the earliest commercial computer systems, ERMA. At the time the bank employed thousands of workers simply to process checks, and although ERMA would have been a success even if used only to handle the collection and printing of debits and credits, typing in account numbers remained an error-prone task that was costing the company millions of dollars a year. The development of MICR at SRI solved this problem by printing the account information onto the checks in a way that was readable both by machine and humans. After a prototype phase in 1955, General Electric was contracted to build 32 ERMA machines, replacing thousands of workers and setting off a wave of change in the banking industry.

MICR quickly spread to other banks, it could be added to checks with existing print technology using the iron-oxide inks for almost no additional cost. Today laser printer toner cartridges are available with MICR ink for printing your own.