Increasing Secret Data Hiding Capacity in QR Code Using 3 x 3 Subcells

Recently, the use of QR code is becoming increasingly popular such that the majority smart-phone devices nowadays are capable reading them. Based on the development of camera technology in latest smart-phone devices, Teraura et al. proposed a method for hiding an additional data into a fine subcell structure of a monochrome QR code. Based on 3x3 subcells configuration, the cover data is placed at the outer subcells while the embedded data is placed in a single center subcell. In general, QR code reader detects a cell color from its center pixel and such that it is difficult to extract the cover data of a 3 x 3 subcells QR code. This research proposes an alternative method by accommodating different approaches in recognizing a cell color. The subcell selection for embedded data was kept secret by applying pseudorandom to randomize the bit data position in each cell. Experimental results show that using the proposed method, 97% of 3 x 3 subcells QR code can be read by a general QR code reader. It uses 4 subcells to store 4 bits additional data and had embedded data capacity 4 times higher than the method of Teraura et al.