Simply scan the paper and crop a perfect square. Make it kind of small. Use it as a background. Most of the wallpapers above were made this way Harder Wallpapers 1. Find a geometric image to scan.
Bricks work well, as does lined paper.
Scan the picture. Crop the picture so that the items on the ends and top are cut exactly in half. That way they will line up when posted as wallpaper. This is tough. Try doing one on lined paper first for practice.