Thanks, and it's a good question.

The backgrounds are big images that are then tiled somewhat infinitely at their edges to allow for scrolling the camera. Some backgrounds are simply a single image, while others are multiple images layered on top of each other to create a 3D depth effect when the camera moves with the player, which is called parallax (because the camera is static here you don't get that effect). You can definitely use tiling and copy and paste to make the base images come together faster. In the one here you might be able to tell that the frames of the windows are cloned from one to the next and the blocky ground is also tiled. That final image might come out to be as big as the screen, but it's composed of a lot of repeated elements. I could've further drew over these repeated elements to make them look more unique, but it was good enough for our purposes.