In the cold season of the year (at least in the northern parts of earth) you might like to fit your twitter background to the present weather conditions.
Here's a small collection of photos I made and that you are free to use for your twitter background or desktop picture. Size of the photos is 1200*900 pixels.
Just click on a photo to enlarge it and then right-click your mouse to download it (for windows users).
If you need to resize a photo you can use some software like paint.net (needs microsoft framework) or picresizer.
The pic below is size 700*525 pixels. It's purpose is for sharing on stumbleupon etc.