1. A method for determining if a user of a computer system is a human, the method comprising the steps of: receiving, by one or more processors, an indication that a computer security program is needed, and in response, acquiring, by one or more processors, at least one image depicting a first string of characters including at least a first set of one or more characters, and a second set of one or more characters; wherein each character of the first set of one or more characters is an alphanumeric character; and wherein each character of the second set of one or more characters is illegible; assigning, by one or more processors, a first substitute character to be used as input for each of the second set of one or more characters, wherein the first substitute character is a different character than any of the second set of one or more characters; presenting, by one or more processors, the at least one image, an indication of the first substitute character, and an indication of when to use the first substitute character to the user, wherein presenting the at least one image, an indication of the first substitute character, and an indication of when to use the first substitute character to the user comprises: presenting, by one or more processors, the at least one image, a description of the first substitute character, and an indication of when to use the first substitute character to the use; and receiving, by one or more processors, a second string of characters from the user; determining, by one or more processors, whether the second string of characters substantially matches, within a predetermined threshold, the first string of characters based on the first substitute character assigned to each of the second set of one or more characters, wherein the determination further comprises: comparing, by one or more processors, each character of the second string of characters to a respective character within the first string of characters, according to character locations within each string of characters; and associating, by one or more processors, a weighting factor to each character of the second string of characters based on the comparison and the set of one or more characters within which the respective character of the first string of characters is a member; and determining, by one or more processors, that the second string of characters substantially matches, within a second predetermined threshold, the first string of characters, based on the weighting factor associated with each character within the second string of characters, and responsive to determining that the second string of characters substantially matches, within a second predetermined threshold, the first string of characters, based on the weighting factor associated with each character within the second string of characters, determining, by one or more processors, that the user of the computer system is a human.