A method for determining boundaries of a rectangular moving image region having a rectangular external shape displayed in a part of a display region (100,200) on the basis of determinations using respective display frames, the method comprising: determining if a first rectangular moving image region in a frame at first time t1 is detected based on a difference to a frame at a different time, if it is determined that the first rectangular moving image region is detected, then retaining the boundary coordinates of the first rectangular moving image region of the first time tl; determining if a second rectangular moving image region in a frame at second time t2 is detected based on a difference to a frame at a different time, if it is determined that the second rectangular moving image region is detected, determining whether the second rectangular moving image region in the frame of the second time t2 is located inside a region specified by the boundary coordinates of the rectangular moving image region of the first time tl; if it is determined that the second rectangular moving image region is located inside, determining whether there is a box at the boundary coordinates of the frame of the first time t1 in a frame of third time t3 based on pixel values of the frame at the third time t3, without using the frame of the first time tl; and if it is determined that there is a box at the third time t3, judging that the region specified by the boundary coordinates of the rectangular moving image region of the first time t1 is a moving region in the frame of the second time t2, wherein t1, t2 and, t3 satisfy t1 < t3 <= t2. determining if a first rectangular moving image region in a frame at first time t1 is detected based on a difference to a frame at a different time, if it is determined that the first rectangular moving image region is detected, then retaining the boundary coordinates of the first rectangular moving image region of the first time tl; determining if a second rectangular moving image region in a frame at second time t2 is detected based on a difference to a frame at a different time, if it is determined that the second rectangular moving image region is detected, determining whether the second rectangular moving image region in the frame of the second time t2 is located inside a region specified by the boundary coordinates of the rectangular moving image region of the first time tl; if it is determined that the second rectangular moving image region is located inside, determining whether there is a box at the boundary coordinates of the frame of the first time t1 in a frame of third time t3 based on pixel values of the frame at the third time t3, without using the frame of the first time tl; and if it is determined that there is a box at the third time t3, judging that the region specified by the boundary coordinates of the rectangular moving image region of the first time t1 is a moving region in the frame of the second time t2, if it is determined that the second rectangular moving image region is detected, determining whether the second rectangular moving image region in the frame of the second time t2 is located inside a region specified by the boundary coordinates of the rectangular moving image region of the first time tl; if it is determined that the second rectangular moving image region is located inside, determining whether there is a box at the boundary coordinates of the frame of the first time t1 in a frame of third time t3 based on pixel values of the frame at the third time t3, without using the frame of the first time tl; and if it is determined that there is a box at the third time t3, judging that the region specified by the boundary coordinates of the rectangular moving image region of the first time t1 is a moving region in the frame of the second time t2, wherein t1, t2 and, t3 satisfy t1 < t3 <= t2.