It is possible to prevent the deterioration of device characteristic as much as possible. A third module selectively generates an engine start allow signal based on the first and second engine start flags. The threshold calculation unit is designed to estimate, on the basis of a first and second division of a reference image which corresponds to the digital image into first and second subareas, a background luminance value for each first subarea and an object luminance value for each second subarea. The viral gaming event may continue to spread to numerous gaming machines.