OMR

Optical Mark Recognition (OMR) is a scanning process of recognizing markings on a page. An example of an OMR application would be a test answer sheet on which you shade the answer "bubbles" with a pencil.

OCR

Optical Character Recognition (OCR) is the process of taking a scanned image and recognizing the text.

ICR

Intelligent Character Recognition (ICR) is an advanced form of Optical Character Recognition(OCR).