In CrazyTalk 8 you can work with traditional 2D heads or the new 3D heads. Both work slightly different with backgrounds.
For 3D heads when you create a custom head there will be no background present. If you add a background from the template library and want to remove it you can do so from Create > Atmosphere Settings on the Menu Bar. Just deactivate the background by taking the check out of the box.
For 2D heads you can remove the background from a photo by clicking the Mask Editing button on the top toolbar. This is the same as was in CrazyTalk 7. Again if you have already added a custom background from the library and want to remove it, just go to File > Background Settings on the Menu Bar and select Actor Only.
Once you have your 2D or 3D ready with the background removed, you can export in Sequence Image PNG format. This will export with a transparent background and the images can then be compiled in any video editing software. If you need the audio from your project as well you can export this in WAV format.
I hope this helps give you a little guidance.