1. An image processing apparatus comprising: an interpreter unit configured to interpret control programs including a command train; a memory unit configured to store predetermined function programs for controlling a function of the image processing apparatus, the function programs being defined as an interface between the control programs and a device driver program for controlling the function and being used commonly by the control programs, the device driver program operating a printer engine; and an execution unit configured to execute the device driver program in accordance with the interpretation of the control programs by said interpreter unit, wherein, in execution of the device driver program, the execution unit controls the printer engine in a manner based on a version of the interpreter unit.