A method for determining a foreground image and a background image, the method includes the following steps, generating a characteristic data of each of N sub-region images of in an interested region of N parent images, classifying the N sub-region images to image groups of in M image groups according to the characteristic data of each of the N sub-region images, obtaining a motion level of each of the M image groups according to a motion area of in the N sub-region images, determining whether each the image group belongs to a background image group or a foreground image group according to each the motion level of each the image group and an image quantity of in each the image group. The method can correctly determine a foreground image and a background image, even a foreground object stops moving and stays in a viewable range of an image apparatus.