thats because its a picture. a drawing, you think its 3d like a doll house, but its not, its flat like a piece of papir. you are not able to put him behind it, because there is nothing to put him behind, you need to make an overlay and upload it
I recomand you to watch this video
(26) EPISODE: All about overlays - YouTube
btw, I am sorry if I seem rude, I am not good at explain things in a friendly way, its the landguage barrier,