1. An apparatus for detecting an object, comprising: a filter which filters a current input image and a background model generated based on a previous input image; a homography matrix estimation unit which estimates a homography matrix between the current input image and the background model; an image alignment unit which converts the background model by applying the homography matrix to a filtered background model, and aligns a converted background model and a filtered current input image; and a foreground/background detection unit which detects a foreground by comparing corresponding pixels between the converted background model and the filtered current input image.