I print my own railroad backdrops from images that I google. Here I show roughly how I do it.
My railroad is based on scenery in Northern California, so I google well known landmarks around the Bay Area for photos. I make heavy use of the clone tool to blend and extend the different photos. Once I have a complete section, I bit-trace the image (using an old copy of Flash MX) so that they look de-focused, more like they are painted rather than photographs. Once I print them out, they look sorta like watercolor drawings.
One of the reasons that I de-focus the photos is so that they don’t distract from the trains themselves.