A method is to be implemented by an online education system, and includes: when it is determined based on image data received from a teacher-end device that an image contains an image portion which corresponds to a body part above a chest of a teacher, determining whether one of a facial expression, a facial movement, a face position, and a body portion between a chin and the chest of the teacher satisfies a predetermined condition by performing image recognition on an image data portion of the image data which corresponds to the image portion; and when a result of the determination is affirmative, transmitting a notification message to the teacher-end device for output of the same by the teacher-end device.