Today, most Internet applications still establish user authentication with traditional text based passwords. Designing a secure as well as a user-friendly password-based method has been on the agenda of security researchers for a long time. On one hand, there are password manager programs which facilitate generating site-specific strong passwords from a single user password to eliminate the memory burden due to multiple passwords. On the other hand, there are studies exploring the viability of graphical passwords as a more secure and user-friendly alternative. In this paper, we present GPEX, a password manager program implemented as a web browser plug-in to enable using graphical passwords to secure Internet applications without any need to change their authentication interface. Experimental results show that GPEX has security and usability advantages over other password manager plug-ins. specifically; we find that with the visual interface of GPEX, users have a more complete and accurate mental model of the system and incorrect login attempts causing security exposures can easily be avoided.