1. An image forming system comprising: an image forming apparatus; and a server that is connected to the image forming apparatus; the image forming apparatus including a model-unique-information transmitting unit that transmits model-unique information of the image forming apparatus to the server, and a function-control mediating unit that controls functions of respective units based on an instruction from the server when an application corresponding to the model-unique information transmitted to the server is executed at the server; and the server including a model-unique-information receiving unit that receives the model-unique information transmitted by the model-unique-information transmitting unit of the image forming apparatus, an application managing unit that manages and executes the application corresponding to the model-unique information acquired by the model-unique-information receiving unit, and an interface unit that instructs the function-control mediating unit of the image forming apparatus to perform control corresponding to the model-unique information, based on an instruction of the control on a function of the image forming apparatus from the application executed by the application managing unit.