QR Codes for Information Hiding by Hybrid Halftone Dots

Quick Response (QR) Code is a matrix-type two-dimensional barcode composed of black and white modules. Nowadays, QR Codes are commonly used as access media for product promotion, tracking and tracing, authentication, and other purposes. However, QR Codes printed on materials not only occupy a space but are susceptible to counterfeiting. Thus, we introduced hybrid halftone dots into QR Codes invisible to the human eye at a certain distance but scannable by devices for information hiding. In the QR Code, black modules are represented by Amplitude Modulation (AM) dots, while white modules are represented by Frequency Modulation (FM) dots. By balancing the area of FM and AM dots through adjustment, hybrid halftone dot QR Codes with different ratios of FM and AM dots are generated. The minimum dot area is scanned by smartphones to evaluate the effectiveness of information hiding. The Finder Patterns and hybrid halftone dot QR Codes were tested to enhance the effectiveness of information hiding. The research results indicated that the designed hybrid halftone dot QR Codes showed innovative effectiveness in information hiding. The lower the dot area percentage of hybrid dot QR Codes, the better the effectiveness of information hiding. Moreover, QR Codes with documents can be used to conceal finder patterns.