The three-dimensional (3-D) Fourier transform of the nonaccelerating object in an image sequence lies on a plane passing through the origin of the 3-D frequency domain. Instead of using a 3-D frequency planar filter, we propose a new filter design technique for object tracking using a one-dimensional trajectory filter-in the spatiotemporal domain. This filter can track a moving object with linear or nonlinear trajectory without prior knowledge of the target trajectory. Also, it is easy to design and has a very low computational complexity. More importantly, it can be implemented in real time.