I've been working on an animation trying to incorporate animation into the background images.I don't know the reason why it won't render the arm. I tracked and solved the motion in the movie clip editor, and here's how it renders:
I'm using blender render and not cycles.Items that I figured probably aren't as important are blurred out a little, so it's easier to see what settings I have.
If anyone can help please do. Here are some settings of that part of the arm that shows up in the render as transparent: