Q: FCPX: Image movement

I was wondering how I could make images run smoother in FCPX. Like say you add an image to someones face in the video, and that person starts walking a certain direction, how can I make the image run smoothly instead of it cutting every frame to where I want it to be? Because when I try to do it, I just move the image every couple frames or so and it turns out really choppy and not good.