1. A method implemented on a computer comprising the steps of: receiving, at the computer, a first string of alphanumeric characters; breaking the first string of alphanumeric characters into multiple pieces; assigning the multiple pieces of the first string of alphanumeric characters to a first number of pre-chosen image categories, wherein the first number of pre-chosen image categories are chosen and sequentially ordered by a user and each one of the pre-chosen image categories comprise a group of images sharing a common attribute perceived by a human; randomly selecting images from the first number of pre-chosen image categories; assigning dummy pieces of alphanumeric characters to a second number of image categories not selected by the user, and facilitating presentation of a matrix of the randomly selected images from the first number of image categories and the second number of image categories to the user, wherein images in the first number of image categories correspond to more than one alphanumeric character and at least one of the images in the first number of images categories correspond to both a number character and alphabetic character, wherein images in the first number of image categories are configured to be selected by a user tapping or selecting the images without entering the corresponding alphanumeric character.