Cant set tracked footage as Background??

Hi, i have my tracked footage and i solved it and everything. But for some reason when i click apply as background. It doesnt do anything. Have a look for yourself:

I am trying to learn blender so im gonna watch tutorials too get good then start my own projects. I have watched : Blender guru beginner tutorial, and currently watching CG GEEK CGI tutorial.

Any good recomendations for blender tutorials on youtube?