US Patent 7154531 Detecting objects by digital imaging device

A system for detecting objects includes a digital image device such as CCD camera to control a defined area for unauthorized intrusions. The digital imaging device views a predetermined pattern positioned across the defined area from the device. A processor periodically compares an image stored in the memory with a digital representation of the predetermined pattern, and a signal is sent to a control unit when the correlation is missing as a result of the object entering field of vision of the digital imaging device and obscuring said predetermined pattern.