If you're using images, you must edit the backgrounds out before you bring them into Anime Studio.
So for example, if you drew a face in another program and you don't want the blank space around the face to show up in Anime Studio, then you need to set the background to transparent in the program you drew it in and export it in a format that supports transparency.
Download gimp and import your image to it. If your image isn't white here is a simple way.
Under layers add a transparency alpha layer.
Then click on the area u want to not show.
Go to edit and hit clear.
Save file as PNG.
I only done this a few times and gimp is a rather complex program but u can get some help from You Tube tutorials or hit the help tab on gimb and it send you to their tutorials.
Also, you will see the outline of the box in editing but when u render its not there.