Thank you!

KZfaq comments are the worst place to ask questions like this. The fastest way to get a good answer is blender.stackexchange.com/ To explain it: You'll need the following nodes: Mask (Fixed), Transform, Scale and Mix... You see? KZfaq comments are really the worst place for this. But here's the answer you need: blender.stackexchange.com/a/2404/15678

Good question. I've loaded the PNG from Blender to Photoshop and created a mask from transparency. There's a small dilation inside Blender's image. It's only 2 pixels and not enough to use for mipmapping but better than the white backdrop from photoshop.