1. A method of comparing working and reference images stored as digital data comprising: extracting a plurality of line segment data from the digital data representing the working image, the extracted line segments being noncontiguous and having a relative positional relationship among themselves, wherein said extracted data for each line segment comprises data for each pixel in that line segment of said working image; comparing each extracted line segment with digital data representing the reference image to identify, by location within said reference image, every line segment from said digital data of said reference image which matches each extracted line segment from said working image to a predetermined degree; and determining that the working and reference images are identical if a match is found for each of said extracted line segments of said working image, wherein the positional relationship among matching line segments from said reference image match said relative positional relationship among said extracted line segments from said working image to a predetermined degree.