Abstract or Summary:
In recent years, several graphical password methods have been proposed in which a set of images is employed in place of a password string as the user’s key. In terms of memorability, graphical passwords are superior to conventional authentication using random string passwords; however, because the images occupy a large amount of space on the screen, they remain weak against shoulder surfing. To mitigate this risk, unclear images generated by alpha blending, filtering, or hybrid imaging of original images can be used instead.

In this paper, we analyze the relationship between subjective impressions and our image similarity assessment method in order to avoid using inappropriate background images in generating a hybrid image for a graphical password. Experimental results show that our similarity measure coincides closely with the subjective visibility of the key image within a hybrid image.