47. The computer-readable storage medium of claim 46 wherein the user responds to the test by repeating the textual characters in the character string via an input device after reading the character string from the altered original image.
46. A computer-readable storage medium having stored thereon a data structure for use as a test for distinguishing a human from a machine, said data structure comprising: a plurality of human-readable textual characters randomly selected from a predefined set of available characters; said characters being individually altered to inhibit computerized character recognition, said altered characters being concatenated into a character string, said character string being included in an original image wherein each of the characters of said character string have a particular coloring, said original image being subjected to an operation to further alter the character string and to further inhibit computerized character recognition according to a configurable difficulty factor, said operation adding random arcs to the original image, at least one of said random arcs altering the particular coloring of a segment of at least one of the characters of the character string at least one of said random arcs linking a plurality of the characters, and said altered original image to be rendered to a user as a test having a level of difficulty in computerized character recognition represented by the difficulty factor.