To relatively easily utilize a password which can be easily memorized by a user and cannot be easily predicted by a third person.

A user selects one, two or more reference images from two or more kinds of the reference images and selects a display element from the respective display elements inside the selected reference images. Further, the user selects another reference image and selects a display element. The selection order of the display elements is registered as a selection pattern. When authenticating the user, the user selects and inputs character symbols from the reference image in an order according to the selection pattern set by himself/herself. The character symbol string is transmitted to the authentication system and converted to the selection pattern. The authentication system detects the selection pattern corresponding to the character symbol string, and judges that it is a proper user when detecting the selection pattern related to a user ID among the plurality of detected selection patterns.

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