The major MICR fonts used around the world are E-13B and CMC-7. The E-13B font was chosen by George Jacobi, who was working for General Electric at the time. Almost all US, Canadian, UK and Indian checks now include MICR characters at the bottom of the paper in the E-13B font. Some countries, including France, use the CMC-7 font developed by Bull.
In addition to their unique fonts, MICR characters are printed with a magnetic ink or toner, usually containing iron oxide. Magnetic printing is used so that the characters can be reliably read into a system, even when they have been overprinted with other marks such as cancellation stamps. The characters are first magnetized in the plane of the paper with a North pole on the right of each MICR character. Then they are usually read with a MICR read head which is a device similar in nature to the playback head in an audio tape recorder, and the letterforms' bulbous shapes ensure that each letter produces a unique waveform for the character recognition system to provide a reliable character result. Examples of MICR waveforms have been developed and can be displayed using spreadsheet applications like Microsoft Excel or compatible. (See the following reference. http://hayosh.home.comcast.net/~hayosh/MICR%20Waveforms.htm)
The error rate for the magnetic scanning of the numbers at the bottom of a typical check is smaller than with optical character recognition systems. For well printed MICR, the can't read rate is usually less than 1% while the substitution rate (misread rate) is in the order of 1 per 100,000 characters.
In 1960s, the MICR fonts became a symbol of modernity, leading to the creation of lookalike "computer" typefaces that imitated the appearance of the MICR fonts, but, unlike real MICR fonts, had a full character repertoire.
In 1991, Advantage Laser Products became the first toner cartridge manufacturer to offer MICR toner in lieu of MICR Ink for desktop laser printers. This revolutionized the check printing business. Prior to 1991 checks were printed with magnetic ink on an offset press. With the advent of MICR toner, checks could be printed on almost any desktop laser printer.