You could technically just move really far away and then take pictures of multiple bricks in a single screenshot, followed by editing. This saves issues with typing all the stuff for the datablocks and having a ton of separate images.
Paint.NET also has a green screen plug-in so that solves the transparency issue immediately, even for windows (if you fiddle with settings). The Plug-in is called "Chroma Key".
Just make sure there's not much overlapping going on, as in, you could easily select the shapes through a rectangle.
Also remove vignette.
*Note that if you are not far enough and there are bricks on each side of the viewport rather than centered, they will be affected by fish-eye.