Transparent video background from image
What you're looking for is a difference matte. (Not to be confused with a Color Difference Key which is similar to regular chroma key.) It can certainly be done, though you should know that difference mattes are fairly temperamental.

The way it works is by finding the difference between an image and each frame of video, and removing anything that's the same, while leaving whatever's different. This means you need a locked-down camera when filming and you need a clean plate of the scene without any actors (or whatever you're trying to remove).

I'm not knowledgable in Blender, so I don't know if it's possible there. I haven't used one in a long time, so don't know what the current landscape is for plug-ins or apps that do this.