Abstract: A non-transitory computer-readable storage medium storing a computer program stored in a computer readable storage medium is provided. The computer program causing a computer to prevent an illegal leakage of an image displayed on a display device of the computer includes receiving operation mode information from a server after the computer is booted, determining whether an operation mode of the computer program is a photographing attempt prevention mode or a violation detection mode based on the operation mode information, determining whether communication between the server and the computer is possible, executing the photographing attempt prevention mode when the operation mode is the photographing attempt prevention mode and the communication is possible, and executing forcibly the photographing attempt prevention mode even if the operation mode is the violation detection mode when the operation mode is the violation detection mode and the communication is not possible.