One method of adjusting a focal length of a camera obtains a captured image of the camera by an application server, where a user can log onto the application server and decides if there is a need to adjust the focal length of the camera again. Another method obtains a captured image of the camera by an application server, determines if a quality of the captured image is acceptable by the application server, and sends the determination results to a mobile device. The focal length of the camera is adjusted again by checking the determination result on the mobile device.