This uses special ink which
contains iron particles that can be
magnetised and then read when the printed numbers passes through a MICR reading machine.
The MICR reading machine will
only recognise numbers printed in a standard font using special magnetic ink. This provides a high level of security
because any attempt to alter the magnetic ink printout with normal ink will be ignored.
Because it is expensive, MICR it is mainly used by banks. The account number,
the cheque number and the branch number
are pre-printed on a cheque.
When you receive a cheque and deposit it in your bank they print the amount
and your account details on the cheque in magnetic ink.
It then sent
to a clearing bank to be read by another MICR reading machine and the correct amounts
are automatically transferred between accounts by computers.