As can be seen, the output values of NOR are simply the inverses of the corresponding output values of OR.
The OR (and similarly the NOR) operator typically takes two binary or graylevel images as input, and outputs a third image whose pixel values are just those of the first image, ORed with the corresponding pixels from the second. A variation of this operator takes just a single input image and ORs each pixel with a specified constant value in order to produce the output