Cox [2012] proposed a complicated algorithm to embed a binaryimage into a QR code during the data encoding stage of generating the code. He carefully investigated the internal structure of QR code and the logic behind data encoding, and designed an algorithm to encode image content as redundant numeric strings appended to the original data as shown in Figure 2(b). However, this technique works only for URL type data string and the quality of embedded image is limited by the length of encoded URL. Similarly, Duda [2012] attempted to embed halftone images into QR codes using a constrained coding technique. While a sophisticated analysis of freedom bits is proposed for embedding image pixels,
it currently works for images of monotonic shapes and produces mediocre results. An application of extending to delicate halftone images is not addressed.