1. A label and tag printer comprising: hardware; firmware configured to control functions of the label and tag printer, a first memory storing an application program, and at least one application program interface configured to directly interface with the firmware, the firmware including first source code to perform an initial function of the label and tag printer, the initial function being a function to print a first format of an image on a label, and second source code to perform an extended function of the label and tag printer, the extended function being formatted as the at least one application program interface, the extended function being a function to print a second format of an image on a label, the at least one application program interface including first reference information to call the first source code and second reference information to call the second source code; a processor which is configured to: generate a first software command, by executing the application program, to instruct performing the initial function, call the first source code, by referring to the first reference information in accordance with the generated first software command, perform the initial function, by controlling the hardware in accordance with the first source code, generate a second software command, by executing a modified application program that is a modified version of the application program, to instruct performing the extended function, call the second source code, by referring to the second reference information in accordance with the generated second software command, perform the extended function by controlling the hardware in accordance with the called second source code, build an image buffer on the second memory after a boot-up process of the label and tag printer; generate print data corresponding to the image, by executing the application program on a virtual machine; render the print data to image data, corresponding to the first format and the second format, based on the first source code and the second source code, respectively; write the image data on the image buffer; control the hardware to print the image corresponding to the image data on the image buffer; and purge the modified application program from the second memory and download the modified application program to the first memory after operation of the tag and label printer is concluded, and a second memory having a higher operation speed than that of the first memory, wherein the processor is further configured to expand and write the application program, the at least one application program interface, the virtual machine, and the firmware, which are stored in a compressed format in the first memory prior to the boot-up process of the label and tag printer, on the second memory in an uncompressed format after the boot-up process of the label and tag printer.