Study on an Objective Evaluation Score of Overlapping Images for Graphical Password Using Hybrid Images

Abstract

In our preceding study, we proposed a graphical password using hybrid images. Visibility of the hybrid image depends on the viewing distance and the structural similarity of the image. In addition, the visibility of the foreground image is different depending on the combination of the foreground image and the background image. Therefore, not all hybrid images are suitable for the graphical password. Takahashi et al. proposed an objective evaluation score using Speeded-Up Robust Features (SURF) for choosing appropriate hybrid images. However, their score does not sufficiently consider the visibility of the foreground image for the legitimate user. In this paper, we proposed an objective evaluation score considering the visibility of the foreground image for both the legitimate user and the shoulder-surfer. Experimental results show that our score can choose hybrid images suitable for user authentication.