OMR, definition

"Optical Mark Recognition (OMR) is the process of capturing data by contrasting reflectivity at predetermined positions on a page. By shining a beam of light onto the document the scanner is able to detect a marked area because it reflects less light than an unmarked surface."

"It is generally distinguished from "optical character recognition" (OCR) by the fact that a recognition engine is not required. That is, the marks are constructed in such a way that there is little chance of not reading the marks correctly. This does require the image to have high contrast and an easily-recognizable or irrelevant shape."