Optical mark reader (OMR) reads the presence or absence of a mark on a paper optically. Light is directed on to the paper and the reflected light is analysed for the detection of a mark. If a mark is there on the surface of the paper, that area sends back lesser light are to the OMR. It is used to read multiple choice answers in a test and the data are transferred to a computer for processing.
Optical character reader (OCR) detects shape, and can identify characters. It can examine each character as if it were made up of a collection of minute spots. Once the whole character has been scanned, the pattern detected is matched against a set of patterns stored in the computer. The pattern that matches or nearly matches is taken to be the character read. Patterns that cannot be identified are rejected. It is used in mail sorting and credit card billing.