/3/ - 3DCG

How would I go about having a material render as alpha regardless of what's in the scene in blender?
Not a transparent shader that works with the image, just straight alpha. Like cutting it completely out of the image.

Just for an example, in pic related.
I'd want to have the white bands to render only as straight alpha as a png. So if I opened the entire image, the white bands would show as transparent regardless of what's in the scene. Leaving the background information intact.
Even if part of it were in front of a sphere, the white areas should render as transparent even if it's in front of something.

I'm not sure if blender is able to do something like this. If it is, I'm not really sure how to go about it.
I realize it might be kind of counter productive to try and use this as a solution, but a project of mine needs something like this.