Sparse signal modulation schemes encode a data channel on a host image in a manner that is robust, flexible to achieve perceptual quality constraints, and provides improved data capacity. The host image is printed by any of a variety of means to apply the image, with sparse signal, to an object. After image capture of the object, a decoder processes the captured image to detect and extract data modulated into the sparse signal. The sparse signal may incorporate implicit or explicit synchronization components, which are either formed from the data signal or are complementary to it.

An information embedding device, comprising: a memory; and a processor configured to execute a procedure, the procedure including: from an image, detecting, as an embedding target pixel block, a pixel block having a pixel value that, after being changed by a specific value corresponding to information to be embedded into the image, will be within a first specific range of an average value of pixel values of a surrounding pixel block; and changing the pixel value of the detected embedding target pixel block by the specific value.

A communication system includes a server device and a client device. The server device includes an encoding unit that encodes information about characters contained in a first image to generate an encoded image, a generation unit that generates a second image in which the generated encoded image is embedded at a position specified from a position of the characters on the first image in place of the characters, and a transmission unit that transmits the second image to the client device in response to a request for the first image from the client device. The client device includes an extraction unit that extracts the encoded image from the received second image, a decoding unit that decodes the extracted encoded image, and a replacement unit that replaces the encoded image on the second image with characters specified from decoded information to generate the first image.