1. A computer monitoring method for monitoring a usage state of a computer based on actuation of the computer by an operating system and on recording of a display image displayed on a display apparatus of the computer, the method comprising: acquiring, when data from the operating system or an application program actuated on the operating system is displayed on the display apparatus, a function to be executed by a subsystem that provides a graphics function of the operating system in order to create the display image by acquisition means that uses an input function or an output function of the subsystem; extracting text data from the function by extraction means; storing the text data in association with the function by storage means in a database stored in the computer or in a server connected by a network with the computer; and acquiring at least one of data selected from among an operation history of the application program, an operation history input by way of an input apparatus of the computer, a communication history of the computer, characteristic information of the computer, a raster data output from the subsystem and an execution time of the function; and correlatively storing the same in association with the text data or the function in the database, wherein the acquisition means comprises interface driver means that comprises a function for performing data transmission and reception with a device driver for controlling a device of the computer and a function for providing an interface shared by the operating system and the device driver and that is actuated in a kernel mode of the operating system, the interface driver means provides an interface between the operating system or the application program and the input function or the output function of the subsystem, and the function is acquired by way of the interface of the interface driver means.