1. A method of embedding a bit stream of information into binary images by a computer, the method comprising steps of: setting by the computer a priority of modification for each pixel in the binary image according to how much the modification of the pixel stands out, setting by the computer a lower bound of the order of preference priority of modification according to required strength of the embedding in advance for embedding the information, specifying by the computer a candidate pixel for embedding a bit value of the information by inverting the bit value thereof in the binary image, by making correspondence bit values of the information with pixels of the binary image one by one and comparing each bit value comprising the information to be embedded with the bit value of each pixel, specifying by the computer a pixel to be modified in a case in which the priority of modification of the pixel is equal to or higher than the lower bound of priority, and embedding the information by the computer inverting the values of the specified pixels to be modified.