If you want to make your own custom nature scenes wallpaper, it is important to start with good pictures. While taking pictures of the outdoors may seem simple, getting a shot good enough to put up on your wall takes decent equipment, some basic technique, and a lot of patience.
The first step in taking a good nature picture is having the right equipment. The camera should be either a film or digital SLR, or a great quality snapshot, but the brand and other options are up to you. Lenses are more important than the camera itself so you should buy the best quality lens that you can afford. They vary on snapshot cameras too; some have really nice, sharp high-end lenses, such as Zeiss or Leica, whereas others use far inferior optics, so that's an important part to read up on before investing in a snapshot camera.
For those using an SLR, your subject matter will determine the types of lenses you need. For close-up shots of wildlife, especially smaller animals or those you can only see from a distance, you will need a telephoto lens. A wide-angle lens is more useful for landscape pictures. If you like to take extreme close-ups of plants or insects, you may want a macro lens. Since the best shots are often taken in lower light conditions, lenses with lower apertures are better (but also more expensive). A low aperture will also let you use a faster shutter speed when taking wildlife photos. For foliage or landscapes, shutter speed is not as much of an issue. The last piece of essential equipment is a tripod, which can seem like a lot to carry around, but will make a noticeable difference in your photos.
Once you have your equipment, you can work on your technique. Taking nature photos requires a willingness to explore, and the patience to find the right shot. Be aware of your surroundings, and do not be afraid to take a lot of pictures. Nature shots are generally best taken in the morning or evening, when the natural light provides for the most interesting illumination. Try to get shots from a variety of angles, and unless you are taking a landscape picture, get as close to your subject as you can.
When setting up your shot, remember that simpler is better. You do not want your photos to be too cluttered, especially when they are going to be your wallpaper. Also keep in mind the colors you want your wallpaper to be. In addition, since your pictures will be blown up to cover your wall, you want them to be as clear and sharp as possible. If you are using a digital camera, be sure to set your images to the highest resolution available. If you are using film, go with a really low ASA such as 50 or 100, which needs more light than faster films, but produces nice, sharp images.
Once you're back home again, look through all the pictures you took with a critical eye to determine which would be best for your wallpaper. When you have made your decision, upload the photo to one of the many companies that offer custom wallpapers and place your order. In a few weeks, you will have your own photo covering an entire focal wall in a room, creating a fantastic focal piece and a huge installation of your own art.