You can take any image from 600x800, or rotate an image of 800x600 (as it is a usual size for wallpapers, that can be even better). And you don't need to have Photoshop or the like. You take the image, open it with paint, save it as "BMP, 256 colors) and you're set.
Lazy as I am, I've just googled some 600x800 images on Google (you can set an exact size for your pics in "advanced search"), edited them the way I said and that was it. I doubt to put them 'ere, as it's hard for me to credit them correctly.