1. An image processing apparatus for processing image data which is formed of a predetermined number of pixel data obtained by an image-capturing device including a predetermined number of pixels, the pixels having a time integrating function, said image processing apparatus comprising: amount-of-inter-frame-movement detection means for detecting an amount of movement between frames of a foreground object of a designated frame of the image data based on the designated frame and a frame preceding or subsequent to the designated frame; mixture-ratio detection means for detecting a mixture ratio indicating a ratio of mixture of a foreground object component constituting the foreground object and a background object component constituting a background object in a mixed area in the designated frame, in which the foreground object component and the background object component are mixed; amount-of-movement-within-exposure-time detection means for detecting, in accordance with the mixture ratio, an amount of movement of the foreground object within an exposure time in which the pixel data constituting the image data is obtained; and exposure-time-ratio detection means for detecting a ratio of a time interval of the frames to the exposure time based on the amount of movement between the frames and the amount of movement within the exposure time of the foreground object.